Let's try a few things that frequently fix this sort of issue: * [[Refresh Firefox - reset add-ons and settings]] * [[Troubleshoot Firefox issues caused by malware]] * [[Upgrade your graphics drivers to use hardware acceleration and WebGL]]

Do you see any Firefox processes in the Windows Task Manager? Did you try to delete the parent.lock file in the Firefox profile folder? *http://kb.mozillazine.org/Profile_folder_-_Firefox *C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\Profiles\<profile>\ See also: *http://kb.mozillazine.org/Profile_in_use *https://support.mozilla.org/kb/Firefox+is+already+running+but+is+not+responding Boot the computer in Windows Safe mode with network support (press F8 on the boot screen) to see if that helps in case of problems to delete the parent.lock file. *http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/