To see if another Firefox is still running after closing/shutting down: ending Firefox in the Task Manager is simple. First, open the Task Manager by pressing Ctrl+Shift+Escape. You can also right-click your taskbar and select Task Manager. Firefox won’t appear in the list of running applications because this list only shows applications with open windows. No problem – just click the Processes tab or Details Tab. Once you’ve located firefox.exe, select it and click the End Process button.

Note: This does not solve the issue but only shuts down Firefox. I believe it has something to do with your Profile and something that locks. Try this : https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data Note: Though it is possible something in the Profile is corrupted and has something to do with a lock file. You might need further help with this issue. Then : https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-settings

For updating Firefox please try this : https://support.mozilla.org/en-US/kb/update-failed-error-message-when-updating or https://support.mozilla.org/en-US/kb/update-firefox-latest-version

Please let us know if this solved your issue or if need further assistance.

Thank you, Pkshadow, but I have tried all that you suggested. First thing I did was stop all the processes in task manager, I have also tried to update as soon as I boot up my machine, I have also tried resetting Firefox, I have also tried starting in safe mode, both Firefox and the computer itself, I have tried disabling all the add-ons... So I guess my only option now is to completely uninstall Firefox and install it brand you. My question now is, is there a particular way to uninstall Firefox completely so that it doesn't leave any trace in my system?

It is possible that other software that runs on your computer is keeping a handle on some file in the Firefox program folder. This will prevent Firefox from replacing these locked files to new versions of the files.

You can boot the computer in Windows Safe mode with network support to see if that has effect.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/
• http://www.7tutorials.com/4-ways-boot-safe-mode-windows-10

Thank you, Cor-el, but as I said above, I already tried that. I have also had no problems with other updates.

Try this in case of issues with updating:

• download the Firefox installer and save the file to the desktop
  *https://www.mozilla.org/en-US/firefox/all/
• start the Firefox installation with a double-click on the desktop icon