Firefox’s Nova redesign arrived for Release-channel users with Firefox 157.0 on September 29, 2026. It refreshes the browser’s tabs, toolbars, menus, sidebar, and New Tab page, while adding more theme choices and Compact Mode. You can switch to Mozilla’s Firefox Proton theme for a familiar appearance, but restoring the previous sidebar requires a separate setting and disables vertical tabs.
What Nova is—and which Firefox version includes it
Nova was the internal project name for Mozilla’s redesign; Mozilla presents it publicly as Firefox’s new design. The change is a renewal of Firefox’s interface, not a replacement browser. Mozilla describes it as the browser’s biggest visual refresh in years and, in its Add-ons documentation, its largest interface refresh since Proton in 2021.
Firefox 157.0 was first offered to Release-channel users on September 29, 2026, according to Mozilla’s Firefox 157.0 release notes. Mozilla said the redesign was rolling out across desktop and mobile. The exact experience can vary by platform, but the release notes and launch announcement describe the update as a broad interface refresh rather than a standalone theme.
What changed in the Firefox interface
The redesign updates the visual system and several everyday browser areas together. Mozilla describes refreshed colors, icons, and themes across tabs, toolbars, menus, the sidebar, New Tab, and Private Browsing. The sidebar is more prominent, and Mozilla’s theme compatibility guidance describes vertical tabs as a first-class layout.
Recommended Free Tools
#1 Best Overall
- Theme choices: Built-in light and dark versions, plus a theme picker with additional themes and wallpapers.
- Sidebar and tabs: A refreshed sidebar and support for arranging tabs vertically.
- New Tab shortcuts: A dedicated area to pin and organize shortcuts.
- Compact Mode: A denser toolbar and tab layout intended to leave more room for web content.
These are interface and customization changes; they do not by themselves establish that browsing is faster, more private, or preferred by users.
How Compact Mode works
Compact Mode reduces the size of the toolbar and tabs to free up screen space for pages. Mozilla calls it a returning option (“Compact Mode is back”) and says an auto-compact option is available for smaller screens. It is useful when browser controls take up too much room, but the trade-off is that those controls are more condensed. Mozilla’s launch announcement describes the feature, but does not publish a measured amount of screen space saved.
How to get a more familiar appearance
Switch to the Firefox Proton theme
For a look closer to the previous Proton-era appearance, Mozilla is featuring a Firefox Proton theme in Add-ons Manager. It is a normal theme, not a full version rollback, so you can switch to it or switch away again through the browser’s theme options. Changing the theme does not restore every earlier interface behavior.
Restore the previous sidebar layout
If the sidebar itself is the issue, Firefox 157’s release notes document a separate preference. In the address bar, open about:config, search for sidebar.revamp, and set it to false. This restores the previous sidebar, but it also turns off vertical tabs. Mozilla says the preference will remain available until the end of 2027. This is a sidebar-layout choice, not a switch that reverts the full Nova redesign.
Will existing Firefox themes still work?
Mozilla says themes continue to load and that most color and image properties continue to work, although some may look different. The main change is how the theme is applied across the interface: the sidebar now shares the theme background with the toolbar area, and with vertical tabs, the tab-bar color also applies to the toolbar.
That can affect older theme artwork. An image designed as a narrow horizontal toolbar banner may look awkward when it appears behind a tall vertical sidebar. Mozilla’s theme compatibility guide suggests using backgrounds_area: "top_toolbars" when an image should appear only in top toolbars, setting sidebar colors explicitly, and specifying selected-tab colors because the old selected-tab shadow is gone.
The guide also notes that sidebar expansion on hover may fail to show a theme background in Firefox 157. Mozilla announced Firefox 158 for October 13, 2026, and says that release is scheduled to fix the issue; that date is an announced schedule, not confirmation that the fix has shipped. Other theme adjustments mentioned by Mozilla—including better-fitting focus and link colors, a separate menu and panel icon color, sidebar hover and selected-state colors, and improved tab-strip button hover states—are described as work without release dates, so they should not be treated as already available.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What Mozilla says about performance and privacy
Mozilla’s Firefox UX Team reported that it had improved load times for key page content by 9% over the preceding year. That is Mozilla’s figure for the year before its May 2026 design announcement, not a controlled comparison of Nova with Proton and not an independent benchmark of Firefox 157. Mozilla’s September launch post also says the new design has “no cost to your browser performance”; that is Mozilla’s own product claim, and the materials cited here do not provide independent benchmark results.
Free tools Windows power users keep installed
One-click scans. No signup required.
Mozilla’s design announcement says the refreshed interface brings privacy tools forward, including the built-in VPN and Private Browsing, and describes Settings changes for controls such as turning AI features off and adjusting Enhanced Tracking Protection. Those statements describe interface goals and available controls; making a control easier to find is not evidence that a privacy feature’s effectiveness has changed.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
