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Firefox Nova is no longer only upcoming: Mozilla said the redesign shipped with Firefox 157 in September 2026. To try the early preview, use Firefox Nightly; to inspect the shipped interface, use Firefox 157 or later. Mozilla has not established a supported, current preference for manually enabling Nova in other builds.
Choose the Firefox build that matches what you want to do
| Build | Availability and maturity | Best use |
|---|---|---|
| Firefox Nightly | Mozilla announced the Nova preview on July 8, 2026, and described it as early, with rough or inconsistent areas possible. [Mozilla Connect, July 8, 2026] | Try the preview and follow its changes as Nightly updates. |
| Firefox 157 or later | Mozilla’s September 29, 2026 theme-developer announcement says Nova shipped with Firefox 157. [Mozilla Discourse, September 29, 2026] | Inspect the released interface and its appearance options. |
The sources establish the preview and the Firefox 157 release, not a performance or stability comparison between builds.
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Try Nova in Firefox Nightly
- Install or update Firefox Nightly using Mozilla’s official Firefox channels.
- Open Nightly and inspect the refreshed interface, including its sidebar and tab layout.
- Keep Nightly updated. Mozilla’s July preview announcement said the project was early and warned that some areas could be rough or inconsistent.
Mozilla’s announcement does not provide a formal test protocol. The checks below are practical ways to explore the interface, not official Mozilla testing requirements.
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Inspect the shipped interface in Firefox 157
If you already have Firefox 157 or a later version, look at the Nova layout directly. Mozilla identifies the sidebar and vertical tabs as notable parts of the refresh. You can also try the built-in appearance choices discussed by Mozilla, including Compact Mode, themes, wallpapers, and New Tab customization. [Mozilla Connect discussion]
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Practical checks for everyday use
- Open and close menus, then check whether the controls you use regularly remain easy to find.
- Switch between tabs and try the vertical-tab layout.
- Open and use the sidebar, noting whether its placement and contents suit your workflow.
- Change a theme or wallpaper and check whether the result remains legible across the browser interface.
Check themes in Firefox 157
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 in Nova, particularly around the sidebar and vertical tabs. Background-image themes are more likely to look different. [Mozilla’s theme-developer guidance]
- Install the theme in Firefox 157.
- Inspect the sidebar and vertical-tab layout for color, contrast, and image placement.
- Check any background-image areas as well as the main toolbar; do not assume a theme’s previous appearance will carry over unchanged.
Can you enable Nova with an about:config preference?
A Mozilla Support community discussion reports that setting browser.nova.enabled to false in about:config reverts Nova in the context discussed. That is community advice about turning the interface off, not an official method for enabling or testing Nova. The discussion also cautions that the preference could be removed. Mozilla’s cited announcements do not establish a supported current preference for manually enabling Nova, or its availability across every operating system and build. [Mozilla Support community discussion]
For a preview, use Nightly; for the shipped design, inspect Firefox 157 or later. Avoid relying on a configuration preference as a lasting way to switch Nova on or off.
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