Firefox 157 brings Project Nova, Compact Mode and new media features

Firefox 157’s headline is Project Nova, a desktop redesign that updates Firefox’s browser controls, sidebar and menus—and brings back Compact Mode. The release also focuses on media: Mozilla planned to enable JPEG XL decoding by default, add hardware-accelerated AV1 decoding for WebRTC calls, and improve the display of some HDR video. Release-date reporting is inconsistent: Mozilla’s documentation listed September 29, 2026, as the expected date, while some coverage reported the stable build available on September 28.13715

Project Nova: a refreshed Firefox interface

Nova changes the look of the browser rather than replacing its basic purpose. Tabs and other controls use softer shapes, and the redesign updates the visual style across browser chrome, the sidebar and menus.114

A key practical change is the return of Compact Mode, which reduces interface spacing for people who want browser controls to take up less room. Mozilla describes it as an option for users who prefer a denser interface.14 Coverage of the release also describes Standard and Touch density options, though details may vary by platform.27

Can you switch back to the old Firefox design?

The available sources confirm layout customization, but they do not establish a supported, complete rollback from Nova to the previous interface in Firefox 157. Compact Mode changes spacing; it should not be treated as a switch that restores the old design. An earlier report described a setting for trying Nova before its release, but that does not verify a post-update rollback option.1430

JPEG XL decoding planned by default

Mozilla’s stated plan for Firefox 157 was to enable JPEG XL image decoding by default across platforms. The decoder is jxl-rs, an implementation written in Rust. Mozilla said support had previously been available behind the image.jxl.enabled preference, as well as through a Firefox Labs option.17

That means JPEG XL is a notable compatibility change for Firefox users and sites that serve the format. The source describes Mozilla’s plan for version 157; it does not, by itself, confirm the rollout status on every installation.17

AV1 decoding for WebRTC calls

Firefox 157 adds hardware-accelerated AV1 decoding for WebRTC calls, according to release coverage. WebRTC is used for real-time browser communications, so this change concerns video calls rather than general video playback.7

HDR video fixes

The beta addressed cases where HDR video encoded in 8-bit formats appeared dull or gray, alongside other playback fixes.318 Mozilla’s Firefox roadmap lists HDR video on Windows and Linux, but the available sources do not establish the exact platform-by-platform scope of every Firefox 157 fix.13

Firefox 157 and Mozilla’s release schedule

Firefox 157 entered beta on September 14, 2026.1 It follows Mozilla’s move from a four-week to a two-week release cycle, which began with Firefox 155.15

For the stable release date, the sources do not fully agree: Mozilla’s release documentation listed September 29 as the expected date, while reports published September 28 said the update was already available.715 The clearest summary is that September 29 was the documented schedule, with some outlets reporting availability a day earlier.