I think its not Firefox issue . For me it's windows issue. By the way , open the task manager from your administrative id and try to kill the process. let me know, what's happen.

Did you try to reboot the computer?

Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) as a test.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/

http://kb.mozillazine.org/Profile_in_use

Sorry, the Windows Task Manager changed in Windows 8 and the article needs to be updated for the changed Task Manager layout.

First, when opening the Task Manager, make sure you are viewing all tabs. If you see a More Details button at the bottom, click that.

Then, to find firefox.exe, click the Details tab, which corresponds to the Processes tab from earlier versions of Windows.

I've already tried to reboot and when I go to task manager and try to end the process, I get a message saying: access is denied

jul124 said

I've already tried to reboot and when I go to task manager and try to end the process, I get a message saying: access is denied

I don't know why you would get access denied. Is Firefox starting automatically or in the Administrator account, or are you starting it normally under your user account? This could be a Windows 8 thing (I use Windows 7).

I was using it normally under my user account

Sounds as though there might not be any convenient workaround: http://superuser.com/questions/585073/how-to-overcome-access-denied-when-killing-process-in-windows

Do you exit Firefox using the menu? Meaning either:

• "3-bar" menu button > "power" button - the one in the lower right corner
• File > Exit - if needed, tap the Alt key to activate the menu bar

That may work around some issues with exiting Firefox by clicking a "red X" button.

I always exit Firefox by clicking the red x in the top right corner

Please try using the menu instead. Users who have certain add-ons (for example, the Norton Toolbar extension) or certain settings, are finding that Firefox does not shut down properly when using the "red X" button.

I'll do that in the future But what can I do for now to get back firefox?

Usually when you shut down and restart Windows, Firefox is not running and can be started normally.

Is Firefox set to start automatically with Windows? Microsoft has a utility to investigate what is set to happen at startup: https://technet.microsoft.com/en-us/sysinternals/bb963902.aspx

It's possible that something is firing off a process in your default browser and that is hanging Firefox. You could try switching your default browser to IE (IE may offer to do this when you start it) before shutting down and restarting Windows to see whether that makes any difference.