Hello,

Did you download Firefox from the official web site? If not you should uninstall it and download a fresh copy:

• https://www.mozilla.org/en-US/firefox/new/

Your profile is stored separately from the Firefox install, so a new Firefox install should not affect bookmarks and history. You can always backup your profile by copying the folder as well. In Windows, your profile is stored in: %AppData%\Mozilla\Firefox\Profiles\

Please see the following articles for more information on what is stored in your profile:

• Profiles - Where Firefox stores your bookmarks, passwords and other user data
• http://kb.mozillazine.org/Profile_folder_-_Firefox

Before reinstalling Firefox, you can try these free programs to scan for malware, which work with your existing antivirus software:

• MalwareBytes' Anti-Malware
• AdwCleaner (for more info, see this alternate AdwCleaner download page)
• Anti-Rootkit Utility - TDSSKiller
• Microsoft Safety Scanner
• Hitman Pro
• ESET Online Scanner

Running one or two of the programs should be sufficient depending on the type of malware you have - some of the more complicated ones need further intervention. Further information can be found in the Troubleshoot Firefox issues caused by malware article.

After running the scans and reinstalling Firefox, does your problem still occur? Please report back to us!

Do a clean reinstall and delete the Firefox program folder before (re)installing a fresh copy of the current Firefox release.

• Download the full Firefox installer and save the file to the desktop
  https://www.mozilla.org/en-US/firefox/all.html

If possible uninstall your current Firefox version to cleanup the Windows registry and settings in security software.

• Do NOT remove "personal data" when you uninstall your current Firefox version, because this will remove all profile folders and you lose personal data like bookmarks and passwords including data in profiles created by other Firefox versions.

Remove the Firefox program folder before installing that newly downloaded copy of the Firefox installer.

• (32 bit Windows) "C:\Program Files\Mozilla Firefox\"
• (64 bit Windows) "C:\Program Files (x86)\Mozilla Firefox\"

• It is important to delete the Firefox program folder to remove all the files and make sure that there are no problems with files that were leftover after uninstalling.
• http://kb.mozillazine.org/Uninstalling_Firefox

Your bookmarks and other personal data are stored in the Firefox profile folder and won't be affected by an uninstall and (re)install, but make sure NOT to remove personal data when you uninstall Firefox as that will remove all Firefox profile folders and you lose your personal data.

If you keep having problems then also create a new profile.

• http://kb.mozillazine.org/Profile_folder_-_Firefox
• http://kb.mozillazine.org/Profile_backup

• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Clean_reinstall