Have you cleaned the registry? If you haven't already install ccleaner (free from filehippo). Run the registry cleaner to remove old registry keys. If you have passwords etc backed up run the cleaner also, (go to settings and untick 24 hr option).
Check the uninstall programme inside ccleaner to see if firefox is listed, if so run the uninstaller and repeat both cleans.
Install fresh version of FF.
Sounds like the application has a broken link which is being "remembered", wouldnt hurt to reboot before fresh install of FF.
Check the uninstall programme inside ccleaner to see if firefox is listed, if so run the uninstaller and repeat both cleans.
Install fresh version of FF.
Sounds like the application has a broken link which is being "remembered", wouldnt hurt to reboot before fresh install of FF.

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