Firefox usually stops responding because of a temporary process hang, a troublesome extension or theme, hardware-acceleration trouble, damaged profile data, conflicting security software, or a Windows component problem. Work through these eight fixes in order, testing after each one. The first steps preserve your profile; Refresh Firefox and a new profile are later isolation measures, not the starting point.
What “Firefox is not responding” means
When Windows, macOS or Linux shows Firefox as not responding, the browser process is still running but is not completing normal input or drawing work quickly enough. A single overloaded tab, an extension waiting on a stalled page, a graphics-driver interaction, corrupted startup data or a security product inspecting Firefox traffic can all produce the same symptom. The message alone does not prove that Firefox is infected or that your bookmarks are damaged.
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Before changing anything, note what was happening: whether every window froze or only one tab, whether the problem appears at startup or after opening a particular site, and whether it returns after a restart. If Firefox eventually recovers, save important work and use the built-in diagnostics later in this guide. If it is completely frozen, close it normally first; if that fails, use the operating system’s force-quit command. Unsaved form entries or downloads in progress may be lost when you force the process to close.
Choose the least-destructive fix first
| Action | Effect on personal data | Diagnostic value | Typical effort |
|---|---|---|---|
| Restart Firefox and the computer | Low; unsaved work can be lost if you force-quit | Low, but clears transient state | Minutes |
| Clear cookies, site data and cache | Cookies may sign you out; bookmarks and passwords remain | Moderate for page-loading problems | Minutes |
| Clear the startup cache | Does not remove profile data or add-ons | Useful for interface and startup symptoms | Minutes |
| Troubleshoot Mode | Temporary; normal settings return after the next ordinary launch | High for extension, theme and hardware-acceleration faults | Minutes |
| Reinstall Firefox | Profile data such as bookmarks and passwords is stored separately | Tests damaged program files | Several minutes |
| Refresh Firefox | Keeps core personal data but removes extensions and themes and resets preferences | High for profile configuration problems | Minutes plus reconfiguration |
| New profile | Starts without the old profile’s data until you migrate it | Very high for profile corruption | Longer, especially if migrating data |
| System and malware checks | Depends on the change; review security settings carefully | Useful when Firefox-specific tests fail | Variable |
1. Restart Firefox and your computer
Mozilla’s troubleshooting guidance starts with a restart because it clears a stuck Firefox process and temporary operating-system state without changing your profile.
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- Wait about a minute to see whether Firefox recovers. If it does, save any work.
- Close Firefox from its menu. If the window will not respond, use Task Manager on Windows, Force Quit on macOS or the equivalent process tool on Linux to end Firefox.
- Restart the computer rather than simply signing out. This reloads graphics, networking and security components that Firefox uses.
- Open Firefox and repeat the exact tab-opening or browsing action that triggered the hang. Test before changing another setting.
If the same page freezes Firefox immediately after every restart, leave that tab closed and continue with the cache and isolation tests below.
2. Clear site data, cached files and the startup cache
Clear cookies and temporary cached files
Corrupted site data can make one website or a group of pages appear to hang while loading. In Firefox, open History → Clear recent history. Set the time range to Everything, select Cookies and site data and Temporary cached files and pages, then confirm. Menu wording can vary slightly by operating system and Firefox release.
Clearing cookies signs you out of sites and may remove site-specific choices. It does not erase bookmarks, saved passwords or your browsing history unless you select those categories as well. Reopen Firefox and test the affected site before clearing anything else.
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The startup cache stores compiled interface and startup resources. A bad cache can cause slow or incomplete startup even when ordinary web cache data is healthy.
- Open Help → More Troubleshooting Information. This opens Firefox’s
about:supportpage. - Find the section labeled Try clearing the startup cache and choose Clear startup cache.
- Allow Firefox to restart, then test the same workflow.
Startup-cache clearing is a lower-impact diagnostic: it does not remove your profile data or add-ons. If it helps only briefly, continue to Troubleshoot Mode rather than repeatedly deleting caches.
3. Run Firefox Troubleshoot Mode
Troubleshoot Mode is the most useful early isolation test. Mozilla says it temporarily disables extensions, uses the default theme, turns off hardware acceleration and applies default toolbar settings. Your normal configuration returns when you start Firefox normally again.
- Open the Firefox menu, choose Help → Troubleshoot Mode, and confirm the restart.
- If Firefox cannot stay open long enough to use the menu, hold Shift while starting Firefox and select the Troubleshoot Mode option.
- Reproduce the freeze with the same tabs or site. Avoid changing several other settings during this test.
If Troubleshoot Mode fixes the freeze
An extension, theme or graphics acceleration path is the likely trigger. Restart Firefox normally, open Settings → Extensions & Themes → Extensions, disable every extension, and re-enable them one at a time. Test after each change. When the hang returns, update or remove the extension responsible. If the problem appears only with the normal theme or hardware acceleration, leave the offending option disabled and check for graphics-driver updates.
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If the freeze remains
The cause is less likely to be an add-on or hardware acceleration. Keep your extensions unchanged for now and continue with reinstalling, refreshing or testing a new profile.
4. Reinstall Firefox from the official installer
Reinstallation replaces damaged or incomplete Firefox program files. It is different from Refresh Firefox: reinstalling targets the application files, while Refresh Firefox changes profile configuration.
- Download the current installer from the official Firefox site at firefox.com while Firefox is closed. If Firefox will not load pages, use another browser or another computer to obtain the installer.
- Exit every Firefox window. On Windows, confirm in Task Manager that no Firefox process remains before continuing.
- Uninstall Firefox using your operating system’s Apps or Applications settings. Do not choose an option that removes your personal profile if the uninstaller presents one.
- If the installer or Mozilla’s instructions identify leftover program files, remove only those application folders; leave the profile folder containing bookmarks, passwords and history in place.
- Run the downloaded installer, launch Firefox and repeat the test that previously froze it.
Mozilla documents that the normal uninstall-and-reinstall process does not remove profile data because it is stored separately from the program files. If a fresh installation still freezes, the profile or the wider system is a more likely source.
5. Refresh Firefox
Use Refresh Firefox when Troubleshoot Mode and reinstalling do not resolve the issue, or when Firefox starts but behaves erratically across many sites. Refresh restores the profile to its default state while preserving core personal information.
What Refresh Firefox keeps
- Bookmarks
- Browsing history
- Open tabs and windows
- Saved passwords
- Cookies
- Form autofill information
What it removes or resets
- Installed extensions and themes
- Customized preferences
- Toolbar and other profile settings that differ from Firefox defaults
Record critical preferences, extension names and custom toolbar arrangements before starting. Then open about:support through Help → More Troubleshooting Information, select Refresh Firefox and confirm. If Firefox cannot start normally, the same Refresh button is available from the Troubleshoot Mode screen.
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After the refresh, test Firefox before reinstalling extensions or restoring custom settings. Add extensions back individually; reinstalling all of them at once can reintroduce the original fault and hide which change caused it.
6. Create a new Firefox profile
A profile contains settings, databases, extensions and other user-specific files. If damaged files remain in the old profile, a refresh may not be enough. A new profile provides a clean comparison without immediately destroying the old one.
- Type
about:profilesin the address bar and open the Profile Manager page. If Firefox will not remain open, start its Profile Manager from the operating system shortcut or command provided by your Firefox installation. - Choose Create a New Profile, give it a clear name such as Test, and finish the wizard.
- Launch Firefox with the new profile and test the same tabs, sites and downloads. Do not install extensions yet.
- If the new profile is stable, add only the data and extensions you need, testing after each addition. Keep the original profile until you have confirmed that the migration is complete.
A new profile initially lacks the old profile’s bookmarks, passwords, history and other data. Migrate selectively rather than copying the entire profile folder, because copying every file can bring the corruption back. If both profiles freeze in the same way, the problem is probably outside profile data.
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7. Use Firefox’s built-in diagnostics before making further changes
Find a tab or extension consuming resources
Enter about:performance or about:processes in the address bar. These pages expose Firefox’s internal task information. Look for a tab, extension or process using unusually high CPU or memory while the slowdown occurs. Close the specific tab or disable the identified extension, then retest. Resource usage changes with the page and workload, so treat the display as evidence for this session rather than a permanent ranking.
Record the technical state in about:support
Open about:support and record the Firefox version, profile location, installed add-ons, graphics information, hardware-acceleration state, security software entries, crash reports and modified preferences. This record helps you compare a working and failing profile and gives support staff actionable details. Avoid posting personal profile paths or other identifying information publicly.
Diagnostics are especially valuable before Refresh Firefox or profile migration. They can show that a freeze began after an update, is limited to a graphics path, or occurs alongside a particular security product, allowing you to target the next step instead of repeatedly resetting Firefox.
8. Check system conflicts and malware
If Firefox still hangs after the Firefox-specific tests, investigate software outside the browser. Mozilla lists internet-security software conflicts, incomplete Microsoft Visual C++ runtime components on Windows and malware among possible causes.
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Open your security product’s application or firewall list and confirm that Firefox is allowed to communicate. If the security product recently updated, temporarily pause its web-inspection feature only long enough to test, following the product’s own safety guidance. Restore protection immediately after the test. Do not browse unprotected for ordinary use, and do not interpret a temporary improvement as proof that security software is defective; update or reconfigure it through the vendor’s supported settings.
Repair the Windows Visual C++ runtime when relevant
On Windows, Firefox may fail or become unstable when required runtime components are incomplete, including the VCRUNTIME140_1.dll component. Install the current Microsoft Visual C++ Redistributable appropriate for your Windows architecture from Microsoft, restart the computer and test Firefox again. This check is Windows-specific; it does not apply to macOS or Linux.
Run a reputable malware scan
Use your operating system’s trusted security tools or another reputable malware scanner and allow it to update its definitions first. Remove or quarantine anything it identifies according to the scanner’s instructions, restart, and test Firefox. A clean scan does not rule out every software conflict, but it removes one important external cause from consideration.
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How to decide what to do next
- Only one website freezes: clear that site’s cookies and cached files, then test in Troubleshoot Mode.
- Firefox freezes as soon as it opens: clear the startup cache, start in Troubleshoot Mode and inspect
about:support. - Troubleshoot Mode works: isolate extensions, the theme or hardware acceleration one change at a time.
- Reinstall changes nothing: Refresh Firefox, then compare with a new profile.
- Two clean profiles freeze: investigate graphics drivers, security software, Windows runtime components and malware rather than repeatedly resetting Firefox.
- A recent update preceded the problem: record the version and crash details in
about:supportbefore seeking Mozilla support.
What not to do
- Do not delete the entire Firefox profile as a first response; it contains passwords, bookmarks and other personal data.
- Do not clear every History category when the symptom is limited to one site; cookies and temporary cached files are the targeted choices.
- Do not reinstall all extensions immediately after a refresh or profile test.
- Do not disable antivirus or firewall protection permanently to work around a freeze.
- Do not assume a successful startup proves the issue is gone; repeat the workflow that originally triggered the hang.
When to seek further help
Contact Mozilla support after recording the Firefox version, operating system, crash reports, add-ons, graphics state and exact reproduction steps from about:support. Include whether Troubleshoot Mode and a clean profile changed the behavior. That information distinguishes an extension conflict from a system-level failure and prevents support from asking you to repeat tests you have already completed.
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