See what landed recently in Firefox Nightly!

Starting with Firefox Nightly 135, the DevTools toolbox colors have been updated to have higher contrast than the regular theme when in High Contrast Mode. Note that this change will only be activated when all of these conditions are met:

• High Contrast Mode is enabled for the system.
• In about:settings, in the "Colors" popup, "Use system colors" is checked, and "Override the colors specified by the page with your selections above" is set to something else than "Never".
• In DevTools settings, the selected Theme is "Auto".

Starting with Firefox 136, profile management is now available in Nightly builds. Users can now more easily create and switch between different profiles.

Starting with Firefox 137, you can now you can easily add your signatures to PDFs. Draw, type, or upload your signature, then place it exactly where you want. Save your go-to signatures for next time.

Firefox for Android now supports TLS client authentication certificates. When a TLS server requests authentication from the browser, Firefox can now make use of the client certificates that have been added to your Android device.

Desktop mode in Firefox for Android is now enabled by default on tablets, but can still be disabled from the Site Settings.

You can now copy links for background tabs using the tabstrip context menu on MacOS and Linux.

Firefox on Windows 11 now uses acrylic-style menus for popup windows, which better match the operating system’s aesthetic. Users who wish to customize this behavior can do so via the widget.windows.mica.popups preference.

Firefox for Android now allows you to share a downloaded file or its original URL from the Downloads screen.

Fix for MFSA 2025-19 included in 2025-03-26 builds and newer.

Starting with Firefox Nightly 135, third-party tracking cookies are now protected by Total Cookie Protection instead of being blocked by default.

Rededicated previous color settings to Contrast Control settings. (Learn more)

Added support for the error.captureStackTrace extension to avoid incompatibility with other browsers. (Learn more)

Starting with Firefox 138, H265 decoding for WebCodecs is now enabled for Nightly Linux builds.

Starting with Firefox 137, H265 decoding for WebCodecs is now enabled for Nightly MacOS builds.

We have implemented support for Error.isError, which allows for brand checking whether or not an object is an instance of Error. (Learn more)

Starting with Firefox 138, window.getSelection().toString() now correctly returns the text serialization when text is selected in a text control on Nightly builds.

Starting with Firefox 136, scroll-driven animations is enabled in Nightly builds.

Starting with Firefox 137, the Temporal proposal is enabled by default in Firefox Nightly, please experiment with it and provide feedback. Temporal is a better version of Date, for more details, please see https://tc39.es/proposal-temporal/docs/.

Applications can now set their preferred degradation method to be utilized when encoding the configured frame rate and resolution cannot be maintained. (Learn more)

Introduced support for Import Attributes, allowing developers to specify additional metadata when importing modules.

Firefox now enables the cache directive for the Clear-Site-Data header, allowing websites to clear the networking cache. The header gives websites more control over data stored for their users, such as clearing the network cache during logout, mitigating the risk of privacy leaks. (Learn more)