Hello charlesclay, You can try launching Firefox from it's executable in C:\Program Files\Mozilla Firefox - but it won't make it an installed program. Have you tried a Clean Install? See this article: Firefox keeps crashing at startup and scroll down to Try A Clean Install.

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

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

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 the current Firefox version, because this will remove all profile folders and you lose personal data like bookmarks and passwords including personal data in profiles created by other Firefox versions

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

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

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

Your personal data like bookmarks is stored in the Firefox profile folder, so you won't lose personal data when you reinstall or update Firefox, 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 you can create a new profile to test if your current profile is causing the problem.

• https://support.mozilla.org/en-US/kb/Profiles
• https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

Reinstall Firefox

• https://support.mozilla.org/en-US/kb/troubleshoot-and-diagnose-firefox-problems

Thanks Both Unfortunately I cannot get a clean install. I could not get windows 7 to uninstall properly. It removed the shortcut but left the program folder. I have removed the program folder but the firefox installer now just fails to do its job, spending most of its time "not responding" with virtually no cpu activity. It managed to do nearly 2 of the green passes on screen before giving up completely! I clearly need to remove more files but have no tool to do it with! I have tried CC Cleaner to no avail

Hi charlesclay, Other than registry entries, the program files indicated by @cor-el are the only relevent files. Did you try disabling your anti-virus?

If it still doesn't install you can try Norton Utilities 16 to clean up your registry. This is a fully functional 30-day trial and is much more aggressive than CCleaner. When you run the Registry Scan you will probably be alarmed at how much CCleaner has missed. When I first ran it, it found over 5200 invalid registry entries. Norton Utilities 16 (Direct Download Link)

Yes Norton16 sorted me out but i still cannot access my old book marks. I know it should be easy but everytime I copy the .sqlite files across my new profile firefox stops working. I have spent 3 days messing around, so am just going to start a fresh.