Browser interfaces tend to settle into patterns that users learn over long periods of use, so larger visual changes often arrive only after extended testing periods in pre-release channels.
When those updates reach the stable release, the practical differences usually show up first in spacing, icon style, and the amount of screen area left for pages themselves.
'Firefox 157' reached the release channel on September 29, 2026, and includes the interface update Mozilla has referred to internally as "Project Nova."
The announcement describes it as a modernization of toolbars, the sidebar, menus, and related elements, built on an updated design system. Rounded shapes appear on tabs and the address bar, icons were adjusted for both light and dark themes, and the color palette draws on warmer tones paired with deeper purples.
Mozilla states that the same design language now applies across desktop and mobile versions, and that the changes carry no measured cost to browser performance.
A theme picker offers several built-in options, each available in light and dark variants, along with additional wallpapers.
Compact Mode returns as a selectable density setting under Appearance preferences.
This feature is design to reduce spacing in the toolbar and tabs so more of the window is available for page content, with an automatic option that activates on smaller screens.
The release notes note that the mode is intended for use on compact displays and in split-screen arrangements.
During Nightly testing, users reported that the denser layout was preferred by some who did not want the refreshed spacing to reduce the visible area of pages, and that feedback led to the setting being exposed directly rather than left only as an advanced preference.
Other items in the 157 release notes include hardware-accelerated AV1 decoding for WebRTC video calls on devices that support it, replacing software decoding in those cases.
A warning now appears in the site information panel and in Settings if the browser has been configured to record encryption keys.
Firefox Suggest address-bar suggestions expanded to additional European countries and can be controlled in settings.
Amazon is no longer listed as a built-in search engine, though it can still be added manually.
The updated sidebar is enabled by default, while the prior sidebar layout remains available for now by setting the preference sidebar.revamp to false in about:config; that option is scheduled to remain until the end of 2027 and also disables vertical tabs.
Page-level dialogs, color pickers, and autocomplete menus now follow the light or dark scheme of the site being viewed. Separate fixes address video orientation in calls, HDR display on Windows, audio-video sync when playback speed changes repeatedly, and the visibility of the taskbar during full-screen video.
Users who prefer the previous appearance can currently disable the Nova interface by setting browser.nova.enabled to false in about:config.
Support for Windows 8.1 and earlier, and for macOS 10.14 and earlier, ended with this release, with those systems directed to the Extended Support Release channel. The update also contains the usual set of security fixes listed in Mozilla’s advisory for the version.
Reception so far has been mixed in public comments.
Some users have welcomed the return of a denser layout and the additional theme choices, while others have described the rounded elements and gradient accents as a departure from the interface they had grown used to.
Several posts on discussion forums and social platforms have circulated the about:config steps for disabling Nova, indicating that a portion of the existing user base is testing the change and then reverting. Mozilla has not published adoption figures for the new density modes or for the theme picker.
Over the next release cycles the practical effect of the refresh will depend on how often the Compact setting is selected and whether further spacing or color adjustments appear in response to ongoing feedback.
Firefox 158 is scheduled for October, and the release notes for that version will show whether any of the visual or density options receive further changes.
