If Firefox is slow, reinstalling it may help when its program files are damaged—but it is not a guaranteed speed fix. A standard reinstall replaces Firefox’s application files and normally leaves your bookmarks and passwords in the separate Firefox profile. If the problem is caused by extensions or profile settings, try Troubleshoot Mode, Refresh Firefox, or a new profile instead. Back up important data before making a consequential change.
Choose the repair that matches the problem
First identify what is slow: startup, particular pages, or Firefox overall. High CPU or memory use, hangs, and failure to open can point to different causes. If the whole PC is sluggish, reinstalling Firefox alone may not address it. Mozilla lists browser version, video drivers, and hardware resource use among possible contributors to slow performance.
| Repair | Best fit | Effect on data and settings | What it changes |
|---|---|---|---|
| Reinstall Firefox | Suspected damaged or missing program files | Profile data, including bookmarks and passwords, is normally retained | Firefox application files |
| Refresh Firefox | Problematic extensions, themes, or settings | Retains bookmarks, browsing and download history, passwords, cookies, form autofill, and personal dictionary; removes extensions, themes, permissions, modified preferences, added search engines, and other customizations | Creates a new profile and saves the former one on the desktop as “Old Firefox Data” |
| Create a new profile | The problem may be tied to old profile data | Starts without the old profile’s data; keep the old profile available while recovering anything you need | Creates a separate profile for testing |
Mozilla Support says, “Some Firefox issues can be caused by a problem with one of the Firefox program files.” That makes a reinstall reasonable when the application files are suspect, not a universal remedy for slow browsing. (Mozilla’s troubleshooting and diagnosis guide.)
Try low-disruption checks before reinstalling
- Restart the PC and check Firefox for updates. An update or restart may resolve a temporary problem.
- Find resource-heavy tabs or extensions. In Firefox, open
about:processesor Firefox Task Manager and check whether a tab or extension is using unusually high resources. Close or investigate the item rather than assuming the whole browser needs reinstalling. - Test Troubleshoot Mode. Open the Firefox menu, choose Help, then Troubleshoot Mode, and restart when prompted. This temporarily disables extensions and themes and hardware acceleration. If Firefox works better, investigate those add-ons or settings before reinstalling.
- Clear the startup cache if startup is the issue. Open Menu > Help > More Troubleshooting Information, then select Clear startup cache and restart Firefox. Mozilla’s Troubleshooting Information guidance says this does not change profile data or add-ons.
For Mozilla’s current performance guidance, see Quick fixes if your Firefox slows down. Interface labels can vary by release; consult Mozilla’s current instructions if a menu item is not where expected.
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Will uninstalling Firefox delete my profile?
Mozilla separates the Firefox program files from the profile, where personal browsing data and settings are stored. Its standard clean reinstall procedure removes program files, not profile data such as bookmarks and passwords. That separation is useful, but it is not a backup: back up important information before proceeding, especially if Firefox is already damaged or the data is irreplaceable. Mozilla’s installation help lists instructions for backing up and restoring a Firefox profile.
For an important repair, copy the profile using Mozilla’s instructions and store the backup somewhere separate from the PC if possible. Do not delete a profile folder while removing the application; the program folders used in the reinstall steps below are different.
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Use Refresh Firefox when profile settings or add-ons are the likely cause
Refresh is a profile reset, not simply another way to reinstall the application. Mozilla says it creates a new profile while retaining bookmarks, browsing and download history, passwords, cookies, web form autofill, and the personal dictionary. It removes extensions and themes, website permissions, modified preferences, added search engines, and other customizations.
- Open Menu > Help > More Troubleshooting Information.
- Select Refresh Firefox and confirm the prompt.
- After Firefox opens, check your retained data and reinstall only the extensions you still need.
- Decide deliberately whether to keep or delete the desktop folder named Old Firefox Data. It contains the former profile and may include sensitive information.
Mozilla’s Refresh instructions, updated April 9, 2026, warn that the feature may be unavailable with the new profile management system unless Firefox is updated to version 150 or later; the page identifies April 21, 2026, as that release date. If the button is missing, check Mozilla’s current Refresh Firefox instructions rather than assuming the same workflow applies to every installation.
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Reinstall Firefox on Windows
Use Mozilla’s official Windows installer route below. Mozilla also documents installing Firefox from the Microsoft Store on Windows 10 and Windows 11; the source establishes that route and requirement, but not that Store and Mozilla-installer installations have identical update or management behavior. See How to install Firefox on Windows for the available options. For a full offline installer with custom options, use Mozilla’s separate custom-install instructions linked from that page.
- Download the installer. Save the latest Firefox installer from Mozilla’s official download page: mozilla.org/firefox/new.
- Exit Firefox. Close all Firefox windows before uninstalling.
- Uninstall the application. In Windows, open Settings > Apps > Installed apps (or Apps & features on some Windows versions), find Mozilla Firefox, and choose Uninstall.
- Remove leftover program files only if needed. If the Firefox program folder remains after uninstalling, Mozilla lists
C:Program FilesMozilla FirefoxandC:Program Files (x86)Mozilla Firefoxas usual locations. Remove the Firefox program folder if it remains. Do not remove the profile folder. - Run the saved installer. Follow the prompts, then launch Firefox.
Mozilla’s instructions state that this reinstall removes Firefox program files while leaving profile data in its separate location. For a Windows message that says the installation seems incomplete or corrupt, first consider backing up, then check available disk space and the PC’s disk and hardware setup. If an ordinary reinstall does not resolve the error, Mozilla describes a clean installation that removes leftover Firefox program-folder files and restarts the computer before reinstalling. Follow Mozilla’s incomplete or corrupt installation guidance for that error.
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Check performance after the repair
Repeat the task that originally showed the slowdown—such as opening the same pages or starting Firefox—and compare the same symptom. Check about:processes again for a tab or extension consuming resources. If the issue persists, use Troubleshoot Mode and test a new profile; Mozilla notes that profile files can cause problems that Refresh does not remove. Persistent slowness can also involve extensions, profile data, drivers, system resources, or causes outside Firefox. A reinstall by itself does not establish that performance improved.
Mozilla’s troubleshooting guide and Troubleshooting Information page guide describe these diagnostic paths, including trying a new profile when the existing one may be involved.
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