Mozilla has released Mozilla Firefox 147, making the update available ahead of its official announcement scheduled for January 13, 2026. The release focuses on display rendering fixes on Linux, media playback behavior, and a collection of platform-specific improvements that affect performance, privacy, and compatibility.
Linux users running GNOME with Mutter will notice one of the most visible changes. Firefox 147 now matches its window and rendering surface sizes to the actual pixel grid used by the compositor. On fractionally scaled displays, this removes the slight blur that could appear at scaling values such as 125% or 150%. The improvement applies regardless of window size and does not require manual configuration.
Another Linux-related change is support for the Freedesktop.org XDG Base Directory Specification. Firefox now follows standard directory locations more closely, which affects where certain data and configuration files are stored. Users with custom scripts or backups tied to specific paths may want to double-check them after updating.
Media playback receives attention in this release as well. Firefox 147 enables zero-copy hardware-decoded video on AMD GPUs. By reducing unnecessary memory transfers during playback, the browser can lower CPU usage and improve performance, especially when streaming high-resolution video.
Firefox’s phishing and malware protection has also been updated. The browser now supports the Safe Browsing V5 protocol, replacing older versions used to retrieve and process threat data. The change happens in the background and does not alter user-facing controls, but it modernizes how Firefox handles malicious site detection.
On Apple Silicon Macs, Firefox 147 enables WebGPU support by default. This allows websites and web applications to access more advanced GPU features for rendering and compute tasks without relying on experimental settings. The feature is limited to compatible hardware and supported content.
Page loading performance can improve on supported sites thanks to the addition of Compression Dictionaries, based on IETF RFC 9842. This technology allows shared dictionaries to be reused when compressing content, reducing the number of bytes transferred. The benefit is most noticeable on slower or bandwidth-constrained connections.
Firefox 147 also changes how Picture-in-Picture works. When a video is playing in a tab and that tab is sent to the background, Firefox now opens a Picture-in-Picture window automatically. The feature was previously hidden behind Firefox Labs and is now enabled for all users. Those who prefer manual control can adjust Picture-in-Picture behavior in settings.
The browser’s settings layout has been adjusted slightly. Tab-related options are now grouped into Opening, Interaction, and Closing categories. The reorganization does not change existing functionality but makes related options easier to find.
Profile management becomes more accessible in Firefox 147. A new Profiles section appears under General settings, allowing users to create and manage separate profiles for different use cases. Each profile keeps its own bookmarks, passwords, and browsing data, which can help separate work and personal activity or support multiple users on the same system.
With one experimental feature graduating to stable, Firefox Labs gains a replacement. A new “Lists and timer on Firefox Home” experiment adds simple productivity tools to the start page, such as timers and reminders. The feature remains optional and disabled by default.
Several smaller fixes and behavior changes are included. Firefox 147 resolves an issue that caused some HTTP/3 requests with non-UTF-8 headers to time out. Draggable buttons now behave correctly when dragging starts directly on the button, and Accept-Language headers support the same quality values used by other browsers.
Privacy behavior changes for users running Enhanced Tracking Protection in Strict mode. Local network access restrictions are now enabled by default, requiring explicit permission before public websites can reach local network resources. This may affect access to local devices or self-hosted services through the browser.
On Android, Firefox 147 enables Site Isolation by default, aligning mobile protection against certain side-channel attacks with desktop Firefox. On Windows, the update improves compatibility with some monitors that previously caused tab selection problems.
Developer tools also receive incremental updates. View Transitions now expose related pseudo-elements and animations more clearly, the JSON viewer can send resources directly to Firefox Profiler, and CSS tooling improves support for pseudo-elements, anchor positioning, and position-try fallbacks. Firefox 147 also expands standards support, including new CSS features, Navigation API support, module service workers, Unicode 17, and additional locales.
Mozilla plans to formally announce Firefox 147 alongside new ESR releases on January 13, 2026. Installation packages for supported platforms are already available, and users affected by the Linux rendering changes or updated privacy defaults may want to review settings after upgrading.
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