Quick Answer
Firefox 157 is a broad visual update that introduces Mozilla’s Project Nova design, new themes, and a compact layout option. Mozilla began offering the release on September 29, 2026, across desktop and mobile devices. Update Firefox normally, then review the sidebar and Search settings because the redesigned sidebar changes vertical tabs and Amazon is no longer built in.
Key Takeaways
- Firefox 157 began reaching Release-channel users on September 29, 2026.
- Project Nova refreshes Firefox toolbars, menus, the sidebar, and individual browser features.
- New light and dark themes join a compact mode that reduces tab and toolbar spacing.
- The old sidebar can temporarily return through the end of 2027, but doing so disables vertical tabs.
- Amazon is no longer a built-in search engine, although users can add it manually.
What is Firefox 157’s Project Nova redesign?
Firefox 157 introduces Project Nova, a browser-wide visual refresh that Mozilla describes as its biggest design update in years. The update changes the appearance of browser toolbars, menus, the sidebar, and individual Firefox features, rather than limiting the redesign to a single setting or page. Mozilla’s Firefox 157 release notes list the interface changes alongside the release’s technical updates.
Project Nova matters because browser chrome, the controls surrounding a webpage, is present during nearly every task. Changes to spacing, menus, tabs, and sidebars can make Firefox feel more current and can also alter where familiar controls appear. Mozilla said the redesigned interface began rolling out to Firefox users across desktop and mobile devices on September 29, 2026.
Firefox 157 does not change the basic purpose of the browser. Bookmarks, tabs, extensions, search settings, and privacy controls remain central Firefox features, but some controls may look different or occupy different positions after the update. The practical response is to spend a few minutes reviewing the browser layout before changing preferences that may only need time to become familiar.
How do the new Firefox 157 themes and compact mode work?
Firefox 157 adds built-in light and dark themes and restores a compact mode that reduces spacing around tabs and toolbars. Mozilla says compact mode returned in response to user demand, which gives users a supported way to fit more browser controls and web content into a smaller display area. Mozilla’s Project Nova announcement describes the themes and the broader interface rollout.
Compact mode is most useful on laptops, smaller external displays, and setups where many tabs remain open throughout the day. Reducing empty space can leave more vertical room for a webpage, especially when a browser window is not maximized. The limitation is that smaller spacing can make tabs and toolbar targets feel more crowded for users who prefer a less dense layout.
Firefox 157’s theme options also give users a direct way to choose between lighter and darker browser surfaces without relying only on the operating system’s appearance. The most sensible approach is to select the layout that makes tabs, menus, and active-page indicators easiest to read during normal use. A visual refresh should improve usability, not require users to accept a less comfortable layout.
| Firefox 157 interface option | What it changes | Who benefits most | Main limitation |
|---|---|---|---|
| Project Nova | Refreshes toolbars, menus, the sidebar, and individual features | Users who want Firefox’s current interface | Familiar controls can look different after the update |
| Light and dark themes | Changes the browser’s built-in visual appearance | Users who prefer a specific brightness level | Theme choice does not change browser features |
| Compact mode | Reduces tab and toolbar spacing | Laptop and smaller-screen users | Controls can appear denser |
| Refreshed sidebar | Uses the new Project Nova sidebar design | Users who use sidebar tools or vertical tabs | Returning to the old sidebar disables vertical tabs |
What changed in the Firefox 157 sidebar?
Firefox 157 enables the refreshed sidebar for all users, making the Project Nova layout the standard sidebar experience. The sidebar is important because it can hold browser tools while leaving the main webpage visible, and Firefox’s vertical tabs depend on the refreshed sidebar design. Mozilla’s release notes confirm that vertical tabs are disabled when users switch back to the older sidebar.
Firefox 157 still provides a temporary fallback for users who strongly prefer the previous sidebar. Users can set sidebar.revamp to false in about:config to restore the old sidebar, but Mozilla says that preference remains available only through the end of 2027. The fallback is therefore a transition option, not a permanent alternative interface.
The practical tradeoff is clear: users can retain the older sidebar for a limited period, or keep the new sidebar and continue using vertical tabs. Vertical tabs can be especially helpful when many pages are open because page titles can remain more readable in a vertical list. Users who are evaluating a new tab layout can also consider how other browser interface changes affect precise text copying controls and similar everyday navigation tasks.
How can users restore the old Firefox sidebar?
Firefox 157 users can temporarily restore the old sidebar by changing the sidebar.revamp preference to false in about:config. Mozilla states that the setting restores the previous sidebar, but the change also disables vertical tabs. The preference is scheduled to remain available only through the end of 2027, so users should treat it as a short-term adjustment while deciding whether to adopt the new interface.
- Open Firefox and enter about:config in the address bar.
- Search for the sidebar.revamp preference.
- Set sidebar.revamp to false to restore the old sidebar.
- Keep the refreshed sidebar enabled if you want to use vertical tabs.
- Review the layout again before the end of 2027 because Mozilla says the fallback preference will not remain available indefinitely.
Firefox sidebar customization is a low-risk preference change, but users should avoid changing unrelated about:config entries. Advanced configuration preferences can affect browser behavior in ways that are not obvious from the preference name. Stop after changing the named sidebar setting, and use Mozilla support resources if Firefox begins behaving unexpectedly after unrelated configuration changes.
What performance and video fixes does Firefox 157 include?
Firefox 157 adds hardware AV1 decoding for WebRTC video calls on supported devices. AV1 is a video codec, and hardware decoding means compatible device components can handle AV1 video rather than requiring Firefox to decode every stream in software. The change can improve efficiency during supported video calls, although the benefit depends on the device and its available hardware support.
Firefox 157 also fixes a Windows issue that could make some 8-bit HDR videos appear dull or gray. The release fixes another Windows problem that could leave the taskbar visible over full-screen video. These corrections matter because color accuracy and full-screen playback are basic expectations for video viewing, particularly on displays designed to show HDR content.
Firefox 157 does not guarantee that every WebRTC call will use hardware AV1 decoding or that every video service will send AV1 video. Video platforms, call participants, device hardware, and browser support all affect the codec and playback path used in a session. Users who experience persistent heat during video calls should also check broader phone overheating causes, because browser efficiency is only one part of device temperature management.
Why did Firefox 157 remove Amazon from built-in search?
Firefox 157 no longer includes Amazon as a built-in search engine, although users can still add Amazon manually through Firefox Search settings. Mozilla lists the search-engine change in the Firefox 157 release notes, which means users who previously selected Amazon from the browser’s standard search choices may need to add it again if they still want that workflow.
Firefox’s built-in search engines affect where searches from the address bar or search field go by default. Removing Amazon from the default list does not prevent access to Amazon’s website, and it does not prevent a user from adding Amazon manually. The main consequence is convenience: the search option is no longer preconfigured in a newly updated Firefox installation.
Firefox 157 users should open Search settings and confirm their preferred default search engine after updating. Search settings are worth reviewing whenever a browser changes major interface elements because a visual update can make familiar options easier to overlook. Users who want more control over data handling should apply the same caution used for deleting chat history: check the relevant service settings directly rather than assuming an old preference remains unchanged.
What is the Firefox 157 encryption-key warning?
Firefox 157 warns users when encryption-key recording is enabled because the setting can allow other software on the computer to read encrypted web traffic. Mozilla added the warning to make the risk visible before users rely on a configuration that weakens the practical privacy protections provided by encrypted connections.
Encryption-key recording can have legitimate diagnostic uses, but it creates a meaningful privacy risk on a shared, compromised, or poorly secured computer. A program that can access the recorded keys may be able to read traffic that would otherwise remain protected in transit. The warning matters because encryption normally protects data between the browser and a website, while recorded keys can undermine that protection locally.
Firefox 157 users should leave encryption-key recording disabled unless they understand why a trusted troubleshooting process requires it. The practical stop line is straightforward: do not enable key recording to solve an ordinary browsing problem, and contact an organization’s IT or security team before changing the setting on a work-managed computer. Browser safety also depends on responding promptly to security issues, including threats such as fake browser support alerts that attempt to pressure users into installing unwanted software.
Should Firefox users update to version 157?
Firefox users should update to Firefox 157 if they want Mozilla’s current Project Nova design, the refreshed sidebar, compact mode, and the release’s video improvements and Windows fixes. Firefox 157 became available to Release-channel users on September 29, 2026, and Mozilla says the Project Nova design rollout covers desktop and mobile devices.
Firefox 157 is most likely to feel significant for users who spend much of the day managing tabs, using the sidebar, watching video, or joining browser-based calls. Compact mode gives users a practical response if the default spacing feels too large, while the old-sidebar preference provides a temporary adjustment period for users who do not want to adopt the new sidebar immediately.
Firefox 157 users should review three areas after updating: the sidebar, theme and spacing preferences, and Search settings. The most important limitation is that the legacy sidebar option is temporary and disables vertical tabs, so users who rely on vertical tabs should evaluate the refreshed sidebar rather than plan around the fallback indefinitely.
FAQ
When did Firefox 157 launch?
Firefox 157 first became available to Release-channel users on September 29, 2026. Mozilla began rolling out the Project Nova design across desktop and mobile devices on the same date.
Can Firefox 157 users get the old sidebar back?
Firefox 157 users can temporarily restore the old sidebar by setting sidebar.revamp to false in about:config. Mozilla says the preference remains available only through the end of 2027, and the old sidebar disables vertical tabs.
Does Firefox 157 support vertical tabs?
Firefox 157 supports vertical tabs with the refreshed sidebar enabled. Firefox disables vertical tabs when users restore the old sidebar through the sidebar.revamp preference.
Did Firefox 157 remove Amazon search?
Firefox 157 removes Amazon as a built-in search engine. Firefox users can still add Amazon manually in Search settings if they want to use it from the browser.
What does the Firefox 157 encryption-key warning mean?
Firefox 157 warns that encryption-key recording can let other software on a computer read encrypted web traffic. Firefox users should leave the setting disabled unless a trusted technical process specifically requires it.