Firefox 145 release notes for developers (Beta)
This article provides information about the changes in Firefox 145 that affect developers. Firefox 145 is the current Beta version of Firefox and ships on November 11, 2025.
Note: The release notes for this Firefox version are still a work in progress.
Changes for web developers
CSS
-
The
text-autospaceproperty is now supported, allowing automatic spacing adjustments between characters from different scripts (Firefox bug 1981086, Firefox bug 1869577). -
Firefox now supports the legacy
-webkit-fill-availablekeyword as a value for the CSSwidthandheightproperties, to improve web compatibility. This keyword is an alias for the recently-standardizedstretchkeyword (i.e.,width: stretchandheight: stretch) which isn't yet supported in Firefox. (Firefox bug 1988938, Firefox bug 1789477).
HTTP
- The
Integrity-PolicyandIntegrity-Policy-Report-OnlyHTTP headers are now supported for script resources. These allow websites to enforce subresource integrity guarantees for scripts. Note that theendpointskey is not yet supported (violations are logged to console). (Firefox bug 1984973).
APIs
Media, WebRTC, and Web Audio
RTCEncodedVideoFrameandRTCEncodedAudioFrameare now serializable objects, andRTCEncodedAudioFrame()andRTCEncodedVideoFrame()copy constructors are supported. These changes allow frames to be cloned, and to be shared between workers and the main thread. (Firefox bug 1868223 and Firefox bug 1975032).
Changes for add-on developers
- Cookies created with
cookies.set()are now validated, and invalid cookies are rejected. This change was implemented in Nightly only from Firefox 142. (Firefox bug 1976509)
Experimental web features
These features are shipping in Firefox 145 but are disabled by default.
To experiment with them, search for the appropriate preference on the about:config page and set it to true.
You can find more such features on the Experimental features page.
-
CSS anchor positioning (Nightly):
layout.css.anchor-positioning.enabledNightly builds now support CSS anchor positioning by default, which allows to tether elements together. The anchor-positioned elements can then have their size and position set relative to the size and location of the anchor elements to which they are bound. (Firefox bug 1988224).