Firefox Freezes or Hangs at Startup After an Update

Firefox freezing the moment you click it is usually tied to a recent update, an extension built for the old layout, or a graphics driver that cannot start the new rendering path.

Work through the cheap checks first: Troubleshoot Mode, hardware acceleration, and a fresh profile. A clean reinstall comes last, after everything else has failed.

In this guide, I have covered:

Why Firefox freezes or hangs at startup after an update

Your browser worked yesterday. Now Firefox opens to a blank window and sits there after an update.

Firefox moved to a two-week Release cycle in late 2026, so updates land far more often than they used to. Some updates are bigger than a version bump: the Firefox 157 redesign added a new sidebar, a compact toolbar mode, and a refreshed theme. Any of those can clash with an extension, an older graphics driver, or a profile that has been upgraded in place many times.

The usual suspects after an automatic or manual update are extensions built for the old sidebar or toolbar, graphics drivers that cannot start the new rendering path fast enough, and corrupted local storage left by a half-finished update. The fixes below start with the least disruptive checks and end with a full reinstall.

If Firefox is stuck on a “Firefox is updating” splash, end the process first: Task Manager on Windows, Force Quit on macOS. Then come back and start with the version check. We usually start there because a half-installed update explains a lot of these hangs.

Confirm the Firefox version you are stuck on

You need to know which build is actually on disk before you change anything. The page below shows the application version, the build ID, and the update channel side by side.

1. Click the hamburger menu at the top right of the Firefox window.
2. Choose Help, then select About Firefox from the submenu.
3. Look at the line under the Firefox logo that says "Version". The number next to it is your current version.
4. Alternatively, type about:support in the address bar and press Enter. The Version field appears under Application Basics.

If the version is older than the current Release on the mozilla.org Firefox page, the update never finished before Firefox tried to start. That alone can explain the hang.

Install any pending Firefox update

If Firefox launched just long enough to download a new build, finish that update before you try the heavier fixes.

1. Open the Firefox browser app on your computer.
2. Click on the More menu and select the Settings menu.
   
3. Scroll down to the Firefox Updates section within the General tab, and click the Check for updates button.
   
4. Firefox will check for updates and download them. It may ask to restart to complete the installation of the update.
   The browser will be updated to the latest version.

If the browser never updated on its own, install the latest build manually with our guide to download Firefox and update it to the latest version.

After Firefox restarts itself, check the title bar and tab strip for the new layout. If the startup hang comes back on the new build, keep going.

Run Firefox in Troubleshoot Mode

Firefox will not start normally? Troubleshoot Mode launches it with extensions, custom themes, and some hardware acceleration temporarily turned off. If Firefox starts cleanly here, the cause is in your extensions or graphics stack, not in Firefox itself.

1. Click the hamburger menu at the top right of Firefox.
2. Click Help.
3. Select Troubleshoot Mode….
4. Click Restart in the confirmation dialog.

Firefox will offer to keep your extensions disabled on the next normal launch. Re-enable them one at a time using the section below to find the offender.

Turn off hardware acceleration

New Firefox releases sometimes change the rendering pipeline. Older graphics drivers can fail to start the new path, and the window sits on the splash screen indefinitely.

Disabling hardware acceleration pushes Firefox back to a software path. You’ll know it worked when the browser reaches the toolbar and loads your homepage instead of stalling.

1. Click the hamburger menu and choose Settings, then select General from the left sidebar.
2. Scroll to the Performance section.
3. If "Use recommended performance settings" is checked, uncheck it to expose the manual options.
4. Uncheck "Use hardware acceleration when available".
5. Restart Firefox from the hamburger menu so the change takes effect.

Restart Firefox after each switch so the change takes effect. If the hang disappears with hardware acceleration off, leave it off until your GPU driver catches up with the new release.

Disable extensions one by one

An extension that worked fine on the old sidebar or toolbar can deadlock Firefox on the new one. Switch them all off first, then turn them back on one at a time.

1. Open the menu in the top-right corner of Firefox.
2. Select Add-ons and themes from the menu.
3. Click Extensions in the left sidebar to list every installed extension.
4. Click the toggle next to each extension to switch it off.
5. Open the menu and click Exit, then reopen Firefox.
6. If Firefox now starts normally, come back here and re-enable the extensions one at a time, restarting after each.

The last extension you enabled before the hang returns is the one to remove. If every re-enable keeps Firefox responsive, extensions were never the problem.

TIP: Antivirus and password manager extensions hook the deepest parts of startup. Disable those first when you test.

Clear cookies and cached web content

A half-finished update can leave the cache in a state the new browser code refuses to read. Clearing cookies and cached web content forces Firefox to rebuild that data on the next launch.

You will need to sign back into most sites after the clear. It takes a few minutes and rules out corrupted local storage as the cause.

Refresh Firefox

Everything above failed? Refresh Firefox rewrites the profile defaults without touching your bookmarks, saved logins, or browsing history. It is the right next step when the startup hang will not go away.

1. Click the hamburger menu , choose Help, then select More Troubleshooting Information.
2. On the Troubleshooting Information page, find the Give Firefox a Tune Up section on the right.
3. Click Refresh Firefox and confirm by clicking Refresh Firefox in the dialog.
4. Wait for Firefox to restart. Your bookmarks and logins are preserved, but extensions and most site settings are reset.

Refresh takes about a minute, and Firefox restarts into a clean state. If the hang is still there afterwards, profile-level corruption is unlikely to be the cause.

Create a fresh Firefox profile

A new profile shares no data with the broken one, which makes it a clean test. If Firefox starts fine under a fresh profile, the original is damaged beyond what Refresh can repair, and you can migrate individual pieces back later.

1. Type about:profiles into the Firefox address bar and press Enter.
2. Click Create a New Profile and walk through the wizard with the default options.
3. Select the new profile in the list and click Set as default profile.
4. Open the menu, click Exit, then reopen Firefox.

If Firefox starts cleanly under the new profile, copy individual folders (bookmarks, saved logins) back from the old profile listed in the Profile Folder entry on the same page.

TIP: Creating a new profile does not delete the original one, so keep it around as a fallback while you copy data across.

Temporarily restore the classic sidebar

If the hang began right after the redesign update, the new sidebar layout is a likely suspect. Firefox has a preference that turns the sidebar back to its previous layout until the end of 2027. Vertical tabs are disabled as a side effect.

1. Type about:config into the Firefox address bar and press Enter.
2. Click Accept the Risk and Continue on the warning page if it appears.
3. Search for sidebar.revamp in the search box at the top of the page.
4. Click the toggle on the right to set the value to false.
5. Open the menu, click Exit, then reopen Firefox.

If Firefox starts normally now, keep the preference at false and wait for a follow-up update that fixes the new sidebar before switching it back on.

Reinstall Firefox as a last resort

None of the fixes above worked? A clean install replaces every Firefox file outside your profile. Use the official installer so profile data, bookmarks, and saved logins stay in place.

1. Open the menu in the top-right corner of Firefox and click Exit to quit fully.
2. Download the latest installer from the Firefox all-downloads page.
3. Run the installer and follow the prompts to install over the existing copy.
4. On Windows, accept the Use Firefox as your default browser prompt if you want Firefox to stay the default.
5. Launch Firefox from the new shortcut on the desktop or in your Applications folder.

If Firefox still hangs after a clean reinstall, the cause is outside Firefox itself: a security product, malware, or a corrupted operating system library is more likely. Post your symptoms, OS, Firefox version, and the contents of about:support on Mozilla support so a volunteer can take a closer look.

You can also rescue your saved data later with our guide on recovering Firefox data after an update.

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