Mozilla releases Firefox 100: here’s what’s new


The first three-digit version of Mozilla’s Firefox web browser was released on May 3, 2022. Firefox 100 introduces a whole range of new features and improvements, including support for YouTube captions and subtitles for Picture-in -Picture, multi-language spell check, HDR video on Mac and AV1 video decoding with hardware acceleration on Windows.

Firefox 91.9.0 ESR and Firefox 100 for Android are also released. All dev channels also saw a version change. Firefox Beta and Developer 101 and Firefox Nightly 102 editions are now also available.


  • Firefox 100 is the first version on Windows signed with SHA-256. On Windows 7 devices, KB4474419 is required to successfully install Firefox.
  • Some sites or services may crash if they use incorrect user agent parsing. Chromium also hit 100 recently, and this issue applies to all browsers that hit that version. Mozilla has support pages for office and android for users with compatibility issues.
  • Firefox 102 is the next release from ESR.

Firefox 100.0 download and update

firefox 100 about

Firefox 100 is distributed through the browser’s built-in update feature and Mozilla’s website. If you read the article on May 3, it may not be available yet, depending on when you read the article.

Firefox users can run a manual update check to speed up the installation of the new version:

  • Select Menu > Help > About Firefox.

Firefox displays the current installed version and runs an update check. Any update found will be downloaded and installed automatically.

Here are the links to the official download repositories.

New features and improvements in Firefox 100.0

Support for Picture-in-Picture video subtitles

firefox pip subtitles

Firefox’s Picture-in-Picture (PiP) feature has seen several improvements in the new version. It now supports video captions and subtitles on YouTube, Prime Video and Netflix. Simply enable captions in the service’s web interface to see captions and subtitles appear in the browser’s Picture-in-Picture mode as well.

Additionally, PiP supports WebVTT (Web Video Text Track) subtitles, which are supported by sites such as Coursera and Canadian Broadcasting Corporation.

To note: The feature was not enabled by default on a test install of Firefox. I had to set media.videocontrols.picture-in-picture.display-text-tracks.enabled to TRUE on about:config to enable the feature.

Language and spell check improvements

spell check multiple languages ​​firefox

Firefox will warn users when first running the browser if the installed language of the browser does not match the language of the operating system. Users can then choose either language as the display language in the browser.

Firefox’s spellcheck component is now multilingual. Users must install additional dictionaries in the browser to use the feature. Then just right-click on the text field and select or deselect the additional languages ​​under Languages.

Preferred color scheme in settings

firefox website appearance

Firefox users can now select the preferred color scheme for websites. The option is found under Website Appearance on about:preferences.

Options include Firefox theme, system theme, light or dark.

Other Changes

  • Firefox on Mac devices supports HDR video. The first site added by Mozilla is YouTube, but others will follow. It requires Mac OS 11 or newer and an HDR-capable display. Mac users should ensure that “Optimize video streaming on battery power” is not enabled on mobile devices, as the feature will not work in this case.
  • Windows users with at least 11th Generation Intel, AMD RDNA 2 excluding Navi 24 or GeForce 30 processors can benefit from hardware-accelerated AV1 video decoding in Firefox 100. Mozilla notes that installing the Microsoft’s AV1 Video Extension from the Microsoft Store may also be required.
  • On Windows systems with Intel processors, video overlay is enabled to reduce power consumption during video playback.
  • On Twitch, performance when using volume sliders should be noticeably improved.
  • Scrollbars in Windows and Linux do not take up space by default. Firefox follows the system default on Windows, which users can change under System Settings > Accessibility > Visual Effects > Always Show Scrollbars on Windows 10 and 11. On Linux, users can change this in Settings.
  • Firefox supports autofill and UK credit card capture.
  • Firefox ignores several cross-site subresource/iframe request referral policies to improve user privacy by preventing privacy leaks. These include unsafe-url, no-referrer-when-downgrade, and origin-when-cross-origin.
  • On Mac OS 11 and newer, Firefox rasterizes fonts once per window; this should improve new opening and tab switching performance.
  • Progressive reload websites will no longer revalidate all resources.
  • Non-vsync tasks have more time to run, which improves behavior on Google Docs and Twitch.
  • The focus indicator for links changed from a dotted outline to a solid blue outline to unify focus indicators in the browser.
  • Firefox can be set as the default PDF handler when setting Firefox as the default browser.

Developer Changes

  • WebAssembly supports exceptions that can be thrown and caught in WebAssembly or in JavaScript.
  • WritableStream, WritableStreamDefaultWriter, WritableStreamDefaultController, and ReadableStream.pipeTo() are now supported.
  • CSS media features for dynamic range and video dynamic range are now supported.
  • Multiple Java threads can now be profiled.
  • The performance of deeply nested display:grid elements is “significantly improved”.
  • Added Geckoview APIs to control the start and end time of capturing a profile.

Company changes

  • Fixed Symantec DLP compatibility with Firefox.

Known issues

none listed.

Security updates/patches

Security updates are revealed after the official release of the web browser. You find the information published here after release.


Firefox 101 will be released on May 31, 2022 according to the release schedule. Expect at least one point release before Firefox 101.

Firefox extension reviews and news

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Recent Firefox news and tips

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Microsoft roadmap confirms Teams will soon be supported in Firefox

Firefox 99.0.1 maintenance update released

Additional information/sources


Mozilla releases Firefox 100: here's what's new

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Mozilla releases Firefox 100: here’s what’s new

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The first three-digit version of Mozilla’s Firefox web browser was released on May 3, 2022. Firefox 100 introduces a whole range of new features and improvements.


Martin Brinkman


Ghacks Technology News




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