Firefox 139 adds extension page translation, new tab wallpapers, and faster HTTP/3 uploads

Mozilla has released Firefox 139, adding several features and performance enhancements for both users and developers. Responding to widespread requests, full-page translations can now be used within extension pages that start with the moz-extension:// URL scheme. Upload performance over the HTTP/3 protocol has also been notably improved, especially for resumed connections and for those on high-bandwidth or high-delay networks.

Additionally, users can now upload their own images or select any custom color to personalize new tabs. An experimental Link Previews feature has been introduced and can be activated via Firefox Labs in the settings for those interested in early testing. Following these visual updates, pasted PNG images in Firefox will now retain their transparency, addressing a longstanding quality-of-life issue.

On the developer side, the network panel in DevTools now keeps filter settings persistent across Toolbox sessions, directly addressing requests from the Mozilla Connect and Stack Overflow communities. Additionally, the debugger's directory root is now scoped to the specific domain where it was set, preventing cross-domain application and better reflecting typical development workflows.