Hi, Tom. #Go into your Windows Control Panel, then Add or Remove Programs, and make sure Mozilla Firefox is on the list. If it isn't, jump to number 6, if it is, proceed to number 2. #Press CTRL+SHIFT+ESC to open the task manager, and, under the "Processes" tab, make sure "firefox.exe" is not listed. If it is, terminate that process. #Try to start Firefox using the shortcut. If it still doesn't start after, say, 30 seconds (sometimes it takes a bit, specially on slow computers), redo number 2 and proceed to number 4. #Try to run Firefox in [[Safe Mode]]. If that works, you probably have some problem with Add-ons. Disable them all and enable one at a time to find the culprit. If that still doesn't work, proceed to number 5. #Uninstall Firefox (using the "Add and Remove Programs" in your Windows Control Panel). #Download the latest version of Firefox (yes, again) from http://getfirefox.com and install it. #Now try again. If it doesn't work, try [[Safe Mode]]. If that doesn't work either, read [[Managing profiles]] to create a new Firefox profile and see if THAT works. ----- If you do see further crashes on start up, please post the Crash Report IDs here: https://support.mozilla.com/en-US/kb/Mozilla+Crash+Reporter#Viewing_reports_outside_of_Firefox Paste the contents of a few of the text files in the ''submitted'' folder here.