Hello Lsellstrom! I'm sorry for the terribly generic answer, but, have you tried restarting your computer?

Yes of course. That was the first thing I tried. It's very odd because it's as if Firefox is no longer installed on my computer. I couldn't even find it when I did a search for Firefox or Mozilla. But when I tried to reinstall it, my computer said I couldn't do so because it was running. Very strange.

Try to boot the computer in Windows Safe Mode with network support (press F8 on the boot screen or hold down the Shift key) to see if allows to uninstall Firefox. *http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/ *http://www.7tutorials.com/4-ways-boot-safe-mode-windows-10 ---- 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<br>*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 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 uninstall and 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. <hr> *http://kb.mozillazine.org/Profile_folder_-_Firefox *http://kb.mozillazine.org/Profile_backup *http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Clean_reinstall