Firefox 121: Mozilla ends 2023 with a bang

Firefox 121 is the last major release of the Firefox web browser of 2023. The new release introduces major changes, such as AV1 hardware decoding support on Windows, support for voice commands on macOS systems or the switch to Wayland as the default on Linux.

Firefox 121 Stable and Firefox ESR 115.6 are the new versions of the Firefox web browser. All development versions of Firefox are also updated. Firefox Beta and Firefox Developer move to version 122 and Firefox Nightly moves to version 123.

Firefox for Android follows the versioning of Firefox Stable.

Executive Summary

• AV1 hardware encoding support on Windows with Microsoft's AV1 extension.
• Wayland is the default on Linux, which adds all sorts of improvements.
• The native macOS voice commands are supported.
• The new release addresses security issues in the browser.

Firefox 121.0 download and update

All new Firefox updates are available via the browser's built-in updating system. The update is installed automatically on most user systems in the coming days.

Firefox users who don't want to wait for this to happen can install the update manually. Once released, which happens on December 19, 2023, it can be installed directly from within Firefox.

Just select Menu > Help > About Firefox to run a check for updates. Updates found may be installed directly from the page.

Here are the official download locations:

• Firefox Stable download
• Firefox Beta download
• Nightly download
• Firefox ESR download
• Firefox for Android on Google Play

Firefox 121.0 major changes

Wayland Compositor the default on Linux

Firefox uses Wayland Compositor instead of XWayland by default on Linux. Mozilla notes that this "brings support for touchpad & touchscreen gestures, swipe-to-nav, per-monitor DPI settings, improved graphics performance and more.

One limitation is that Picture-in-Picture windows require an additional click or a tweak. The PiP window does not stay in the foreground by default. The issue is discussed extensively on Bugzilla.

Full Extensions support on Firefox for Android

While this has been launched last week, it is still a major development for Firefox on Android. Firefox Stable is no longer limited to a selection of popular extensions. Developers may create extension for the mobile version of Firefox and all Stable users may install them.

This is a major development for Firefox and it could have a positive effect on the browser in the long run. A core reason for that is that it is the only major web browser that supports extensions on mobile.

AV1 Support on Windows

Firefox users on Windows may install the AV1 extension from Microsoft to enable hardware decoding. This is done by visiting about:support, scrolling down to the Media section and activating the "install extension" link next to Av1 there.

This launches the Microsoft Store page of the AV1 Video Extension. You may then install the extension from the Store to add support for hardware decoding in Firefox.

Restart Firefox and recheck the Media section after installation to confirm that hardware decoding is now supported.

Hardware decoding reduces the load on the processor, which may result in performance improvements.

Other changes and fixes

• On systems with macOS, Firefox 121 introduces voice control commands. The commands allow macOS users to interact with their computer using voice. You can, for instance, say "scroll down" or "click done" to get the computer to execute the commands. Apple's support page offers information about the feature.
• Firefox has a new "always underline links" option, which will underline all links that you encounter while using the browser.  You can enable this feature in Settings > General > Browsing > Always underline links.
• A new floating button in the PDF viewer adds an option to PDF documents to delete elements from it.

Developer changes

• Firefox supports the lazy loading of iframes in the new version.
• The text-wrap property was updated with two new values. Balance is used for short content blocks, stable to make sure that editable content does not reflow during editing.
• The :has() selector is now supported.
• The text-indent CSS property supports each-line and hanging property values now.
• The Promise.withResolvers() method is now supported.
• Data.parse() was expanded to support new date formats.
• The sendOrder property of the WebTransportSendStream interface is now supported.
• WebAssembly now supports tail call optimization via new return_call and return_call_indirect alternatives to the call instruction.

Enterprise changes

• Firefox may offer to become the default mailto handler when web-based email services are visited. This can be stopped by setting browser.mailto.prompt.os on about:config to False.
• The Preferences policy was updated to allow disabling the certificates and devices dialogs using the preferences security.disable_button.openCertManage and security.disable_button.openDeviceManager.

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