Firefox 157 ships its biggest visual refresh in years, with a Compact Mode and a sidebar opt-out

Mozilla released Firefox 157 on 29 September 2026, and it looks different. The release notes call it the browser’s biggest visual refresh in years: toolbars, sidebar, menus and individual features move to an updated design system. APH Networks, summarising PC World’s report, says the look is known as Nova, with heavily rounded corners and subtle colour gradients.

Mozilla’s own notes do not use the name Nova in the text, so treat it as the label press coverage has picked up, not an official product name.

What you see after updating

The redesign comes with new built-in themes. The release notes describe light and dark options you can apply in one click, and APH Networks counts 12 themes, each with light and dark variants.

Compact Mode is the other visible change. It reduces spacing in the toolbar and tabs to leave more room for web pages. That matters most on small laptop screens, where a taller toolbar eats a real share of the visible page.

A few smaller changes follow from the redesign:

• Dialogs, colour and date pickers and autocomplete drop-downs now follow the colour scheme of the page, light or dark.
• Pressing Tab now moves focus straight to the address and search text field. The search engine button is reached with Shift+Tab, which is a habit change for keyboard users.
• Amazon is no longer a built-in search engine, though you can add it back as a custom one.

The sidebar: you can undo it, for now

The updated sidebar is now the default for everyone, and the “Show sidebar” setting has been removed. Anyone who preferred the old arrangement has a workaround: set sidebar.revamp to false in about:config, according to the release notes.

There is a cost. The same setting also turns off vertical tabs. And Mozilla says the option stays available only until the end of 2027, so it is a way to delay the change, not to avoid it. If you rely on vertical tabs, you should test them with the new sidebar before deciding whether to flip the switch.

Not just paint

Beneath the redesign, the notes list some practical changes. Hardware AV1 decoding now works for WebRTC video calls on supported devices, which can reduce load during calls. Several fixes target video: sideways or upside-down phone and tablet video in WebRTC calls, some 8-bit HDR videos that looked grey on Windows, and audio and video drifting out of sync after repeated playback speed changes.

One new safeguard is easy to miss. The site information panel and Settings now warn when Firefox is configured to record encryption keys, which could expose encrypted traffic to other software. That is a debugging feature people forget about, so a visible warning is a sensible addition.

The release also carries security fixes, listed by Mozilla under advisory MFSA 2026-97. APH Networks counts more than 70 vulnerabilities fixed, and says updates are also available for Firefox ESR versions. Firefox Suggest, the address bar suggestion feature, expands to 16 more European countries.

Who should care

Most people will see the change the first time they open the browser after the update, and the practical advice is short. Try Compact Mode if you work on a small screen. Check your keyboard habits around the address bar. If you use vertical tabs, look at the sidebar.revamp trade-off before you change anything.

Administrators of managed fleets should note that APH Networks reports a faster pace: Firefox has moved to a two-week release cycle, with version 158 scheduled for 13 October. Smaller, more frequent updates mean fewer big surprises per release, but they also mean a redesign like this one reaches users quickly, and help-desk screenshots go out of date sooner.

What remains to be seen is how Mozilla treats the sidebar after 2027. The release notes give a date for the opt-out ending but nothing about whether vertical tabs will get a separate setting of their own by then.