Firefox 157 Ships Nova Redesign, Compact Mode and Hardware AV1 Decoding for WebRTC Calls
Mozilla's Firefox 157 brings the Nova visual refresh, a returning compact mode, hardware AV1 decoding in WebRTC, and new CSS support for at-rule() and overscroll-behavior: chain.
Overview
Mozilla released Firefox 157 to Release channel users on September 29, 2026, according to its release notes. The headline change is what Mozilla calls the “biggest visual refresh in years,” a modernized look across the browser’s toolbars, sidebar, menus and individual features. Phoronix refers to the redesign as the Nova UI and notes the release arrives as part of Mozilla’s bi-weekly release cycle.
What Changed in the Interface
- Compact mode. The release notes describe a new compact mode that reduces toolbar and tab spacing to leave more room for web content, useful on smaller screens and in split-screen layouts. gHacks reports that the mode is back after requests from users who wanted more room for web content, and that Mozilla added an auto compact option for smaller screens.
- Themes. gHacks lists a new theme picker with built-in themes in light and dark versions, plus new wallpapers.
- Sidebar. Per Mozilla, the updated sidebar is now enabled for everyone. The previous version can be restored by setting
sidebar.revamptofalseinabout:config, which also turns off vertical tabs, and the release notes say that preference will remain available until the end of 2027. The “Show sidebar” option has been removed from Settings. - Page-level widgets. Mozilla says web page
alert(),confirm()andprompt()dialogs, the color and date pickers, and form autocomplete drop-downs now match the page’s light or dark color scheme, per the release notes. - Keyboard focus. Pressing Tab now moves focus straight to the text field of the address bar and search bar instead of stopping on the search engine button first, per the release notes.
Media and Web Platform
On the engine side, the release notes say WebRTC video calls can now use hardware AV1 decoding on devices that support it, instead of always decoding AV1 video in software. Phoronix adds that, up to now, Firefox was always relying on software decoding for AV1 videos with WebRTC.
Mozilla also lists fixes for video from phones and tablets appearing sideways or upside down in WebRTC calls, for some HDR videos encoded in 8-bit color formats looking dull and gray on Windows, and for audio and video synchronization when repeatedly changing the playback speed of videos, according to the release notes.
For web developers, the release notes report two additions: support for the at-rule() function in @supports, which lets authors detect browser support for specific at-rules such as @supports at-rule(@scope), and support for the chain value of the CSS overscroll-behavior property.
Privacy, Search and Other Changes
- Firefox now shows a warning in the site information panel and in Settings when it has been set up to record its encryption keys, which Mozilla says could let other software on the computer read encrypted web traffic, per the release notes.
- Amazon is no longer included as a built-in search engine, though Mozilla says it can still be added as a custom search engine in the search settings.
- Firefox Suggest now offers address bar suggestions in Austria, Belgium, Czech Republic, Denmark, Finland, Hungary, Ireland, Luxembourg, Netherlands, Norway, Poland, Portugal, Slovakia, Spain, Sweden and Switzerland, according to the release notes.
- Mozilla welcomed contributors whose first code change shipped in this release, 21 of whom it describes as brand new volunteers.
What We Don’t Know
The sources reviewed do not give performance measurements for the new interface or for hardware AV1 decoding, and they do not list which devices and platforms qualify for the hardware path beyond “devices that support it.” Mozilla also says it continues to refine the new design, so further interface changes may follow in later releases.