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Clear out junk files and repair common Windows errorsFree Scan →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Repair Windows errors before they cause bigger problemsFix Now →Firefox’s Nova interface is no longer only upcoming: Mozilla said it shipped with Firefox 157 in September 2026. To see it, use Firefox 157 or later; for the earlier preview, install Firefox Nightly. Mozilla has not established a supported current preference for manually enabling Nova, so avoid relying on an about:config switch as an enablement method.
Where Nova is available
Mozilla first announced Project Nova as an early preview in Firefox Nightly on July 8, 2026. The announcement warned that some parts could be rough or inconsistent and advised users to keep Nightly updated. Later, Mozilla’s September 29, 2026 theme-developer announcement said Nova shipped with Firefox 157.
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| Build | Availability | What it is useful for |
|---|---|---|
| Firefox Nightly | Early preview announced July 8, 2026; Mozilla cautioned that details could be rough or inconsistent. Mozilla Connect | Trying the preview and seeing how the interface develops. |
| Firefox 157 | Mozilla said Nova shipped with this release in an announcement dated September 29, 2026. Mozilla Discourse | Inspecting the shipped interface and built-in appearance options. |
How to try Nova in Firefox
If you use Firefox 157 or later
Update Firefox through its normal update mechanism, then inspect the refreshed interface. Mozilla highlighted the sidebar and vertical tabs as notable parts of Nova. The release discussion also mentions Compact Mode, themes, wallpapers, and New Tab customization as appearance options.
If you want the earlier Nightly preview
- Get Firefox Nightly from Mozilla’s official Firefox channel page.
- Install or launch Nightly, then check for updates so you are running a current build.
- Open Nightly and inspect the interface. Mozilla’s announcement described this as an early preview, not a finished or guaranteed-consistent experience. Read the announcement.
Mozilla’s cited announcement does not provide a formal test procedure. Treat the checks below as practical ways to examine the interface, not as Mozilla’s official protocol.
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Practical checks for the refreshed interface
- Open the sidebar and see how its layout and controls appear.
- Try vertical tabs and switch between tabs to check whether the arrangement suits your workflow.
- Open browser menus and common controls to get a feel for the changed interface.
- Try an available theme or wallpaper, and review New Tab customization and Compact Mode if those options appear in your build.
What theme developers should inspect
Mozilla says themes continue to load and that the extension and theming architecture has not changed. However, theme colors and images may appear in different places, particularly around the sidebar and vertical tabs. Background-image themes are more likely to look different.
- Install your theme in Firefox 157.
- Inspect the sidebar and vertical-tab layout for color and image placement.
- Check any background-image areas, then compare the result with the intended appearance.
These are practical checks based on Mozilla’s guidance, not a claim that every theme will require changes. Mozilla’s theme-developer announcement has the relevant compatibility context.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Can you turn Nova on or off in about:config?
A Mozilla Support community discussion reports that setting browser.nova.enabled to false reverted the interface for some users. That is community guidance about turning Nova off, not an official or verified way to enable it or test it. The discussion also warns the preference might be removed. Mozilla’s announcements do not establish a supported current switch, or confirm that the preference is available across operating systems and builds. See the Mozilla Support discussion.
Do not change the preference expecting it to enable Nova. If you are troubleshooting an interface change, use the Firefox build’s documented appearance controls where available; a community-reported preference may not persist or exist in a later version.
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