Firefox 67 with anti-fingerprinting technique letterboxing

Mozilla Firefox 67 will feature a new anti-fingerprinting technique that protects against certain window-size related fingerprinting methods.
Mozilla plans to integrate the new feature in Firefox 67 but delays may postpone the release. Firefox 67 will be released on May 14, 2019 according to the official release schedule.
The technique comes from experiments that the developers of the Tor browser conducted and is part of the Tor Uplift project that introduces improvements in the Tor browser to Firefox (Tor browser is based on Firefox code).
Window dimensions, especially in maximized state and when windows are resized, may be used for fingerprinting.
Fingerprinting refers to using data provided by the browser, e.g. automatically or by running certain scripts, to profile users. One of the appeals that fingerprinting has is that it does not require access to local storage and that some techniques work across browsers.
Tip: A study analyzed the effectiveness of fingerprinting countermeasures recently.
Maximized or fullscreen windows provide screen width and height information. Fullscreen reveals the actual screen with and height, a maximized window the width and height minus toolbars.
Resized windows on the other hand reveal exact dimensions of the browser window, e.g. 1003×744.
Letterboxing protects better against window size related fingerprinting techniques. It is a method that rounds the content view dynamically using 128×100 pixel steps.
Letterboxing adds margins around the content view of the window and calculates the margin dynamically to ensure that it is applied to resize scenarios as well (and not only when a new window is created).
Setting this up in Firefox

The Firefox preference privacy.resistFingerprinting determines whether anti-fingerprinting is enabled in Firefox. Note that it may render some sites and services unusable or less functional.

Make sure you run at least Firefox 67 (check about:support for the version. Note that this does not appear to have landed in Firefox Nightly atm)
Load about:config in the Firefox address bar.
Confirm that you will be careful.
Search for privacy.resistFingerprinting.

True: Fingerprinting protection is enabled including Letterboxing (as of Firefox 67).
False: Fingerprinting protection is disabled.

You can verify that the protection is in place by visiting Browserleaks or any other site that returns the screen resolution and viewport. Just change the window size a couple of times and reload the page to find out if it rounds the resolution and viewport (it should return a multiple of 128×100 pixels).
You may also notice the margins that Firefox uses when the feature is enabled.
Now You: Have you enabled anti-fingerprinting in your browser?
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fx_cast brings Chromecast streaming to Firefox (early look)

If you use Chromecast, a Google’s device to stream content to displays, e.g. to stream a video from your PC to your television, you may have noticed that Firefox is not officially supported.
Google added native Chromecast support to the company’s Google Chrome browser to cast content, e.g. a browser tab to a connected display. It was necessary to install a Chromecast extension in Chrome previously to do so, but that is no longer the case.
Firefox users who own Chromecast devices could not integrate the device in the browser up until now; this changes with the initial release of fx_cast, an open source browser extension for Firefox that implements the Chrome Sender API in Firefox.
The author of the extension released an initial version of fx_cast on GitHub. Note that it requires installation of the extension and installation of a bridge app on the operating system. The initial release brings support for Mac OS X and Linux only, a Windows binary is not provided.
Firefox Chromecast support

Installation is straightforward. The very first thing you may want to do is install the Firefox extension. You find it under releases on the official project website.
Note: the release is listed as beta and the developer states explicitly that you should expect bugs and that site compatibility is limited at this point in time.
Just click on the “xpi” file and follow the installation dialog to install the extension in Firefox. Mac OS X and Linux users find the Bridge app listed under releases as well. Windows users have the option to compile the binary from source or wait until the developer releases a Windows binary to the public.
Use the new cast button in Firefox’s interface once everything is set up, and the Chromecast installed properly as well.  Another option that you have is to use the cast option in the context menu or the cast button that some services display natively.
The interface displays the connected Chromecast devices and the cast menu to select what to cast to a device that is connected.
The Firefox extension may spoof the user agent as most sites check for Chrome to determine whether to enable cast support for the connecting user. It does so for Netflix only currently, but you may add sites to the whitelist to have the user agent spoofed as well for connections to these sites. The variable <all_urls> adds all sites to the whitelist.

The settings displays a good range of options already. You may change the HTTP server port, enable screen mirroring, or change receiver options in regards to media casting.
Closing Words
The extension is in its early stages of development but it works surprisingly well on some sites. Most users may want to wait until the developer releases a stable build (and Windows binary) before they give it a try though.
Now You: Do you use devices to cast streams or content?
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Never lose text input in Firefox again with Textarea Cache

Textarea Cache is a browser extension for the Firefox web browser that caches text input automatically so that you may recover it if the browser crashes or something else that is unforeseen happens.
Text that you type on the Internet may get lost under certain circumstances. Say you write a long comment on a blog and before you can hit submit, the browser crashes, the page reloads, or the submitting gets stuck somehow.
When you open the page again, you notice that your comment did not get posted and that your text is not available anymore. Your only recourse is to type the text again, or leave the site if you are too annoyed by the loss.
Textarea Cache

Textarea Cache is a caching extension for Firefox that caches text input automatically so that you may recover it at any time.
Ideal in situations in which text that you type becomes unavailable before it is posted on the site. You may also use it to save text that it is not ready for publication yet.
The extension requires access to all sites and browser tabs, and access to adding data to the clipboard. It adds an icon to the main toolbar of the browser that you interact with.
A click on the icon displays an URL selector at the top and the cached content below that. Just select one of the available URLs to display the cached text.
Buttons to copy the text, delete it, or delete all are provided at the bottom. If you experience a loss of text, you simply click on the extension icon, select the right URL, and then Copy to copy it to the clipboard.
You may then paste the copied text to the site again to complete the publication.

Textarea Cache includes several options to customize the functionality. The following options are provided at the time of the review:

Add sites to the ignore list. Three sites, Google Docs Spreadsheets, Slack, and Messenger are listed there by default.
Enable the automatic clearing of cache content (days, hours, minutes).
Change the interval in which text is cached. The default is set to 2000 ms which is 2 seconds.
Various interface display options.
Skip confirm when pasting from context menu.

Closing Words
Textarea Cache is quite the handy extension for Firefox users who type medium to long texts regularly in the browser.
Now You: Did you lose text in the past in your browser of choice? What did you do?
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Firefox 67: automatically unload unused tabs to improve memory

Mozilla plans to introduce a new feature in Firefox 67 Stable that aims to improve the browser’s memory usage in low memory conditions.
Browsers use a lot more memory than they did a decade ago, partly because websites grew significantly in size and partly because browsers changed as well.
It is not uncommon anymore that single tabs may use hundreds of Megabyte of memory, and there are cases where memory usage crosses the 1 Gigabyte mark for individual tabs.
Memory usage, especially on low memory devices, is a priority for browser makers. If you run Firefox or another browser on a 4 Gigabyte or 2 Gigabyte RAM system, you may experience a lot of caching if you open enough or the right kind of sites.
The concept of unloading tabs in the browser to free up memory is not a new one. Extensions like Dormancy, Suspend Background Tabs, BarTab, or Unload Tab for Firefox (all no longer compatible with Firefox 57 or newer), or Lazy Load Tabs, TabMemFree, or Tabs Limiter for Google Chrome, supported the functionality for years
Mozilla improved tab unloading significantly in recent years.
If things go as planned, Firefox 67 will introduce a new feature to unload unused tabs to improve memory. The initial bug report dates back eight years but work on the feature began in earnest just a short while ago.
Mozilla plans to unload tabs in Firefox in low-memory situations to reduce the number of crashes that users experience caused by low-memory. The bug lists another scenario, to free up resources, but it is not clear yet if and how this will be implemented.

Mozilla uses a simple priority list to determine which tabs to unload when the event fires (from lowest to highest)

Regular Tabs
Pinned Tabs
Regular Tabs that Play Audio
Pinned Tabs that Play Audio

The feature is already available in Firefox Nightly. It was turned on by default on my system but you can control it with the preference browser.tabs.unloadOnLowMemory.
True means the feature is enabled, False that it is disabled. It appears that it is available on Windows only at this point because its the only platform that Mozilla can detect low-memory conditions on according to the bug assignee Garbriele Svelto.
Firefox 67 will be released on May 14, 2019 to the Stable channel of the browser according to the release schedule.
Google implemented a similar feature in the company’s Chrome browser. Introduced in 2015, Tab Discarding in Chrome discarded tabs from memory if system memory reached a certain threshold.
Closing Words
Mozilla expects a drop in out-of-memory related crashes in Firefox and plans to monitor these crashes in the coming weeks to test the hypothesis.
Now You: How much memory does your browser use, usually?
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Firefox 65.0.2 fixes a geolocation issue

Mozilla released a new version of the stable version of its web browser Firefox to the public yesterday.
Firefox 65.0.2 is already available as an update for existing Firefox installations.
The new version of Firefox fixes a geolocation issue on Windows.
Most Firefox installations are updated automatically to the new version thanks to the browser’s built-in updating functionality.
Users may select Menu > Help > About Firefox to run a manual check for updates. The same page lists the current version of the web browser. Note that Firefox will download and install the update if you open the About Mozilla Firefox page in the browser.
The new version is also available as a direct download on Mozilla’s website. Note that Mozilla offers a net installer by default which downloads data from Mozilla’s server during the installation. You may also download offline Firefox installers instead.
Firefox 65.0.2

The release notes of Firefox 65.0.2 list only one entry:
Fixed an issue with geolocation services affecting Windows users.
Geolocation is a core API of modern browsers used to determine the location of a device in the world. It is often used by mapping and weather services that rely on the user’s location for functionality, e.g. by displaying the local weather report right away or computing directions.
Firefox gives its users control over the feature. The browser displays a notification to the user when sites try to use the Geolocation functionality. Users may allow or block it, and configure certain sites to permanently make use of it without prompts each time.
Mozilla does not reveal the actual issue that users would experience, only that it did affect geolocation on Windows.
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Firefox: Block sites outside Firefox containers extensions

Block sites outside container is a new extension for the Firefox web browser that extend the container functionality of the browser.
Containers, first introduced as a Test Pilot experiment for Firefox and later on released as the Firefox Multi-Account Containers extension, allow users to separate sites and local date from each other. Useful applications include using Containers to sign-in to multiple accounts, e.g. Gmail, Twitter, or Facebook, at once, or to limit tracking.
Another thing that makes the container functionality great in Firefox is that extension developers may improve it. We reviewed several extensions designed to improve Container functionality in the past: Temporary Containers, Facebook Containers, Containers with Transitions, or Taborama are just a few of the extensions that do so.
Note that you don’t need the Multi-Account Containers extension to use Block sites outside container. You cannot create or manage containers using it though.
Block sites outside container
Block sites outside container introduces two new features to containers in Firefox.

Block any site from loading outside their designated container(s).
Allow sites to run in multiple containers.

The second use case is explained easily. You can force sites to open in specific containers using the Firefox Multi-Account Container extension. What you cannot do using it is specify that you want sites to run in multiple containers only.
Block sites outside container changes that as you may set up rules to allow sites to run in multiple containers exclusively.
The blocking option prevents sites from loading outside their designated container(s). Means: any attempt to load embedded content, say a YouTube video, Twitter or Facebook buttons, or other embedded content, fails.
The extension displays an error page when you attempt to load a site that has been blocked in a particular container.

You may load it in a different container if you have set up a rule that allows the site to load in a different container. Other options on the page include disabling the entire rule set, or to enable the current container in the rule set.
Embedded content is blocked automatically.

Configuration is straightforward but unfortunately a bit clunky. Open the Firefox Add-ons Manager and select the Block sites outside container extension.
Select new rule to create the first rule. Rules use a combination of domain names and containers they are allowed to run in. Add a domain per line and select the containers you want the domain(s) to run in afterward.
A red border means that the sites are not allowed to run in that container; this is the default setting. You need to specify at least one container for the extension to work, unless you want to prevent a site from running in any container or outside of it.
Repeat the process to add new rule sets to the extension. You will notice that each is appended to the bottom of the page; manageability is not great if you set up a lot of rules but you may use the on-page find option of the browser to jump to specific rules quickly.
Another issue that you may run into in the current version is that the container listing gets truncated if the container count reaches certain thresholds.
Rule sets can be deleted or set to inactive at any time in the rules.
Closing Words
Block sites outside container is a useful extension for Firefox users who use Containers in the browser or did not use them because of missing functionality that the extension adds.
Setup is a bit complicated because of how rules are displayed and managed, but it is likely that the developer will address these issues in future versions.
Now You: Do you use Containers?
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Firefox's new Web Compatibility page

Firefox Nightly features a new internal Web Compatibility page that lists Firefox compatibility modifications for Internet sites and services.
While it is usually in the best interest of webmasters and companies to make sure that their sites display and work fine in all popular web browsers, it sometimes is not the case.
Web developers may test a site only in Chrome, the dominating browser when it comes to marketshare, or implement functionality that is only supported by certain browsers.
Browser makers like Mozilla face a tough decision when they notice that certain sites or services don’t work properly in their browsers. While they could ignore incompatible sites, especially if a site uses non-standard technologies, it would fall back to the browser if users of it could not access a site or use certain features.
Making sites compatible in the browser, on the other hand, might send the wrong signal. While that is better from a user perspective, more and more sites might ignore all but the most popular browsers.
Web Compatibility
To make compatibility changes transparent, Mozilla added a new web compatibility page to Firefox (only Nightly for now) as a new about page in Firefox.

You may load the page by pointing Firefox to about:compat. Just type about:compat in the Firefox address bar to display all web compatibility modifications that are active at the time.
Mozilla divides the modifications into user agent overrides and interventions. User Agent overrides change the user agent of Firefox when connections to certain sites are made. Some sites may use the user agent of connecting browsers to block access completely, display a different design, or provide different functionality.
While that is justified sometimes, e.g. when a browser does not support a feature used by the site, it is sometimes used to exclude browsers for other reasons, e.g. because functionality was not tested in certain browsers.
Interventions, on the other hand, are deeper modifications to make sites compatible. Firefox may modify certain code used on these sites to enforce compatibility.
Each compatibility modification links to the bug on [email protected]; click on the link to look up information about the underlying issue.
You may disable modifications with a click on the disable button next to them. The button toggles between disable and enable, so that you may enable the compatibility modification again at a later point in time.
Closing Words
Firefox’s new about:compat page is a useful addition to Firefox that improves transparency when it comes to compatibility modifications made by Firefox. (via Sören)
Mozilla has not revealed a target for the inclusion in stable versions of the web browser.
Now You: Did you run into compatibility issues recently on the Web?
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How to remove DarkMatter Certificates from Firefox

Cyber-security company DarkMatter, based in the United Arab Emirates, applied to become a top-level certificate authority in Mozilla’s root certificate program recently.
Certificates are a cornerstone of today’s Internet; HTTPS ensures that communication is encrypted. A company in control of  a root CA could potentially decrypt traffic that it has access to.
A Reuter’s article links DarkMatter to the United Arab Emirates government and surveillance operations. One such operation, called Karma, saw the team hack iPhones of “hundreds of activists, political leaders, and suspected terrorists” according to Reuters.
The EFF notes that DarkMatter’s “business objectives directly depend on intercepting end-user traffic on behalf of snooping governments”.
DarkMatter controls an intermediary certificate already called QuoVadis. QuoVadis is owned by DigiCert which means that there is some oversight in place currently.
Firefox users, and anyone else who has access to tools to manage certificates, might want to remove the intermediary certificates from the certification store. You may remove the root certificate from Firefox using the same method if Mozilla, or anyone else, goes ahead with the inclusion of the root certificate in Firefox.
Note: As some readers have pointed out, certificates get restored with every update. You may also need to clear a site’s cache if you run into loading issues. See this guide.
Attention: Not all QuoVadis certificates are bad. It is not possible to just exclude some, however. removing the certificates may render some sites unusable.
Removing the certificates

Here is how you can remove certificates from Firefox:

Load about:preferences#privacy in the Firefox address bar to open the Privacy & Security settings.
Scroll down to the Certificates section on the page.
Click on the View Certificates button.
Firefox lists all authorities in an overlay. Scroll down until you find the QuoVadis Limited listing (or any other listing you want to remove).
Select a certificate, it does not matter which. Tip: Hold down Shift to select multiple certificates.
Click on “delete or distrust”.
Select ok to remove the certificate from Firefox.
Repeat steps 5-7 for all other certificates that you want to remove. until the QuoVadis Limited listing is no longer there.

You can follow the discussion and integration of the root certificate on Mozilla’s Bugzilla website and the Firefox Dev Security Policy group on Google Groups.
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Add custom search engines to Firefox

Add custom search engine is a free extension for the Firefox web browser to add any search engine to the Firefox web browser.
Firefox users have quite a few options when it comes to adding search providers to the web browser: add them on Mozilla AMO, run searches on sites to have them added, use the search bar to add Open Search search engines, or use the Mycroft Project website to do so.
Mozilla changed recently how search providers are added to Firefox. The initial version broke important functionality, e.g. the option to add search engines from AMO or MyCroft. These issues have been fixed for the most part.
Add custom search engine

Add Custom Search Engine is a browser extension that adds an option to Firefox to add any Internet search engine to the browser using it.
Just click on the icon that the extension adds to the Firefox toolbar to open the “add custom search engine” dialog.
The basic version requires just two parameters: a name for the search engine and the search URL. You need to replace the search term with the placeholder %s. The best way to go about it is to run a search for TEST on the search engine, copy the URL, and replace TEST with %s, e.g. with
The extension may pick up the favicon automatically but you may specify it if it does not or if you would like to use a different icon. Browse options to pick a local icon are provided as well.
Note: The search engine data is uploaded to temporarily due to a limitation with Firefox WebExtensions before the search engine is added to Firefox.
The search engine is added to the list of supported search engines by Firefox. You can make it the default search engine, add a keyword to it, or run searches using Firefox’s one-off search functionality, or by using the search field if you make use of it.
Add Custom Search Engine supports advanced operators that you may enable on the configuration screen. These add the following options:

Use Post query parameters.
Add a suggest Url so that Firefox may use it to display suggestions using that functionality.
Change the input encoding.
Add a description.

Search engines that you add to Firefox remain available even after you remove the extension. You control all search engines by loading the about:preferences#search in the browser. There you may change the default search engine, enable or disable suggestions, add keywords to search engines, or remove search engines again.
Closing Words
Add Custom Search Engine is a handy extension for Firefox users who have issues adding certain search engines to the browser and users who want more control over the process.
Now You: Which method do you use to add custom search engines to Firefox?
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A first look at Firefox's updated Add-ons Manager

The add-ons manager of the Firefox web browser is an essential component; Firefox users may use it to manage installed extensions, themes, and language packs.
Mozilla is in the process of removing anything that is XUL from Firefox. It plans to launch the new about:config in Firefox 67 that uses web standards, and is working on a new version of about:addons as well.
While it is unclear when that new version will be released in Firefox Stable, it is certain that this is going to happen rather sooner than later.
The organization launched an initial redesign of the add-ons manager in October 2018; this initial wave of changes introduced the cards-based design and made some other changes to the interface without removing any functionality from it. Launched in Firefox 64 Stable, it is currently the default view of about:addons. Mozilla revealed back then that the change was part of a larger process.

Part of the redesign landed in recent Firefox Nightly versions already. You need to change the configuration to unlock the new add-ons manager. Note that it is only partially integrated in Firefox Nightly currently and that some functionality is not available; it is okay to get a first impression but not functional enough to use it to manage add-ons.

Load about:config in the Firefox address bar.
Confirm that you will be careful.
Search for extensions.htmlaboutaddons.enable.
Click on the toggle button to set the preference to True.

A value of True means that Firefox displays about:addons using the upcoming design of the page, a value of False that the old design is used.
The current implementation looks like this.

Mozilla plans several major changes to the page and highlighted those in a mockup. Please note that it is possible that some elements may change during development.
The planned design looks like this:

Mozilla plans to replace the dedicated buttons of the interface, e.g. disable or remove, with a single menu for each installed extension; this leaves more room for extension titles and descriptions.
A click on the menu displays options to toggle the status (enable/disable), to remove, and to open the advanced options.
Active and disabled extensions are separated from each other more clearly in the new manager. The selection of advanced options displays the following interface:

You will notice right away that the information is divided into tabs on the page. The tabs details, preferences, and permissions are displayed when you select advanced options.
Firefox opens the details tab by default in the mockup; whether that is the best option is up for debate considering that users may be more interested in the preferences.
Details lists the description of the extension and links to the developer website, reviews, and an option to leave a review.
The preferences tab lists general options and information only. You may disable the toolbar button here, allow the extension to run in private browsing mode, and control automatic updates.
The actual extension preferences are not found here. A click on “visit website” opens the extension options.

The permissions tab lists all requested permissions. It is unclear at this point in time whether it will be possible to disallow certain permissions. The checkmark buttons next to each permission could indicate that but they could also be just visual indicators.
Closing Words
The redesigned about:addons page is a work in progress. Certain elements may change during development.
I appreciate Mozilla’s attempt to add more information to the management page and the clearer structure of it.
I dislike the requirement to select Menu > Advanced options to display additional information, and that the new tabbed details page adds clicks to the process of opening an extension’s options.
Now You: What is your impression of the new add-ons manager? (via Sören Hentzschel)
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