How to revert to the old Firefox look after the Nova redesign

To revert to the old Firefox look, open about:config, search for browser.nova.enabled and set it to false. After a restart you get back the tabs, colors and icons Firefox had before version 157. But that switch is a short-term fix. A Mozilla engineer has already proposed removing it, so this guide also covers the options that keep working into 2027.

Nova is the Firefox redesign that started rolling out on September 29, 2026 with Firefox 157. If you preferred the previous design, you have four routes. There's the hidden switch, official settings that soften Nova, the Extended Support Release and custom CSS. But each one restores something different and lasts a different amount of time.

What changed in Firefox 157

Firefox 157 replaced the design Firefox had used since 2021 with a new one called Nova. Mozilla calls it the browser's biggest visual refresh in years. According to Mozilla's launch post the update brings:

• softer, more rounded tabs
• redrawn icons for light and dark themes
• rebalanced spacing
• a new palette with deeper purples, warmer light tones and a glow on the active tab
• Compact mode as a regular setting again
• new built-in themes in light and dark versions

Menus, shortcuts and extensions work largely the same way. So mostly the look changed. For many people the problem is the rounder tabs, the extra spacing and the purple tint. For example, users on Mozilla Connect complain that bookmark lists and drop-down menus got more spread out.

Which old look do you want back

"Old Firefox" can mean several different designs. The fixes in this guide revert to the old Firefox look you had until September 2026. That's Proton, the design Firefox used from version 89 to version 156.

If you miss something older, no setting will get it back. Classic Theme Restorer, the add-on people used to restore the pre-2014 look, stopped working with Firefox 57 in 2017. Today only custom CSS comes close to those designs.

Turn off Nova in about:config

The fastest way to revert to the old Firefox look is one hidden preference. It isn't in Settings, but Firefox 157 still includes it.

1. Type about:config in the address bar and press Enter.
2. Click "Accept the Risk and Continue".
3. Search for browser.nova.enabled.
4. Click the toggle button so the value changes from true to false.
5. Restart Firefox if the old tabs don't appear right away.

This brings back the Proton tabs, colors and icons. The built-in PDF viewer has its own switch. If PDFs still open in the new style, search for pdfjs.enableNova and set it to false too.

To undo the change, go back to the same preference and click Reset. Still, some users on Mozilla Connect report that menus stayed spread out even with Nova off. The CSS section below has a fix for that.

How long the Nova switch will keep working

Mozilla hasn't announced a date, so don't count on months. In Bugzilla a Firefox engineer proposed removing the pre-Nova code starting with Nightly 161. He added that it shouldn't happen earlier because Mozilla may run Nova experiments through Firefox 160.

Here's what that means in release dates, according to Mozilla's release calendar:

• Firefox 159 ships on October 27, 2026.
• Firefox 160 ships on November 10, 2026. Expect the switch to work through this version.
• Firefox 161 ships on November 24, 2026. The switch may stop working from here.

The plan isn't final. Mozilla later narrowed the bug to the address bar and gave it no target release. So the switch may keep working for tabs and colors a bit longer. Users in the bug asked for a supported "Classic" option, but there's no sign of one yet. That's why it's best to treat the switch as a bridge. If you want to revert to the old Firefox look for longer, set up one of the options below before it goes away.

Settings that soften Nova without hacks

If you can't revert to the old Firefox look fully, three official options get you closer. None of them restores Proton exactly. But all three survive updates.

Turn on Compact mode

Go to Settings > Appearance > Window density and choose Compact. Toolbars and tabs then take up less space. Mozilla hid Compact mode in Firefox 89 and brought it back as a normal setting in Firefox 157. On smaller screens Firefox now turns it on by itself. It changes spacing only though, not colors or tab shapes.

Install the Proton theme

Mozilla publishes a theme called Proton on its add-ons site. It brings back the flatter colors of the previous design. Open the theme page and click Add to Firefox. To switch back, open Extensions and Themes from the menu, go to Themes and enable the Default theme.

Bring back the old sidebar

Firefox 157 turned on the new sidebar for everyone. To get the previous one, open about:config, search for sidebar.revamp and set it to false. Unlike the Nova switch, this one has a date. The Firefox 157 release notes say the preference stays available until the end of 2027.

But there's a trade-off. Turning off the new sidebar also turns off vertical tabs. If you use vertical tabs, keep the new sidebar.

This table shows what each option brings back and how long you can count on it.

Stay on Firefox ESR 153 to keep the old look until 2027

Firefox ESR is the Extended Support Release that Mozilla makes for organizations such as companies and schools. It's also the only official way to revert to the old Firefox look completely. ESR 153 came out on July 21, 2026, before Nova, so it still uses the previous design. According to Mozilla's ESR schedule it gets security fixes until September 2027. After that Mozilla moves ESR users to version 175.

To switch:

1. Download Firefox ESR from Mozilla's website and install it.
2. Let it create its own profile. Mozilla gives every Firefox installation a separate profile.
3. Sign in to your Mozilla account to sync bookmarks, passwords and history.

Don't open a profile you used in Firefox 157 with ESR 153. Mozilla warns that an older version can corrupt profile data such as bookmarks and history. If Firefox shows that warning, click Create New Profile and bring your data back through sync.

ESR has two downsides. First, it gets security fixes but no new features. And in September 2027 you'll face Nova again, unless Mozilla changes its plans. So ESR buys you about a year.

userChrome.css for a long-term fix

userChrome.css is a file with your own CSS rules that Firefox applies to its interface. After the switch is gone, it's the only way to revert to the old Firefox look on the regular release. It's also the most work. Mozilla doesn't support it. And updates can rename the parts your rules target.

To set it up:

1. In about:config, set toolkit.legacyUserProfileCustomizations.stylesheets to true.
2. Open about:support and click Open Folder next to Profile Folder (Show in Finder on a Mac).
3. Create a folder named chrome there and a text file named userChrome.css inside it.
4. Add your rules and restart Firefox.

First fix the menu spacing. Users on Mozilla Connect shared this rule to make drop-down and bookmark menus dense again:

menupopup > menuitem,
menupopup > menu {
  padding-top: 2px !important;
  padding-bottom: 2px !important;
}

Then change the 2px to taste. People in that thread settled on 3 or 4 pixels.

For a bigger change, community projects already try to turn Nova back into Proton. One example is Firefox-Nova-to-Proton on GitHub. Its author says it isn't a perfect copy and hasn't tried it with vertical tabs. Projects like this are young, so check that one is still updated before you rely on it. And expect to fix your setup after big Firefox updates.

Why you shouldn't go back to Firefox 156

Installing an older version is another way to revert to the old Firefox look, but it isn't worth it. Outdated versions don't get security fixes, so known holes stay open while you browse. You'd also hit the same profile warning as with ESR. If you want the pre-Nova design with security updates, ESR 153 is the safe version of the same idea.

If the redesign was your last straw

For some people Nova is one change too many. If you're thinking about leaving Firefox, compare a few browsers first. Our guide to the best Firefox alternatives covers the main options.

Sigma is one of them. It's a free browser built on Chromium, so Chrome extensions work in it but Firefox add-ons don't. It has a built-in ad blocker, real-time phishing warnings and Private Profiles that keep work and personal accounts apart, each secured with a 12-word recovery phrase. There's also Eclipse, a local AI model that runs on your device and works offline. It has its own design, so it won't look like old Firefox. Try it next to Firefox for a week before you decide.