C:\Program Files\Mozilla Firefox
   C:\ProgramData\Mozilla Firefox
   C:\ProgramData\Mozilla
   C:\Users\username\AppData\Local\Mozilla
   C:\Users\username\AppData\Local\Mozilla Firefox
   C:\Users\username\AppData\Roaming\Mozilla
   C:\Users\username\AppData\Roaming\Mozilla Firefox 

#close all Firefox windows (click Exit from the Firefox or File menu). #Delete the Firefox installation folder, which is located in one of these locations, by default: #*'''Windows:''' #**C:\Program Files\Mozilla Firefox #**C:\Program Files (x86)\Mozilla Firefox #*'''Mac:''' Delete Firefox from the Applications folder. #*'''Linux:''' If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it - see [[Installing Firefox on Linux]]. If you downloaded and installed the binary package from the [http://www.mozilla.org/firefox#desktop Firefox download page], simply remove the folder ''firefox'' in your home directory. ____________________________________________________________________________ Try to start Windows Explorer as administrator by right-clicking its icon. Go to those folders and right-click them. Click Properties and under "Permissions" make sure all read/write permissions are checked. If Windows doesn't allow to enable them, start Windows in Safe Mode. Starting Windows in Safe Mode may prevent your computer from running any malware or tool that may be blocking some administration actions such as removing a folder, modifying a system file, uninstalling a program, etc. To start Windows in Safe Mode under Windows XP, Vista or 7, press F8 repeatedly during reboot until a menu appears, and choose Safe Mode. Under Windows 8 you should start (Windows+R) msconfig, go to Boot and mark "Start on safe mode". Reboot your computer and Windows 8 will run safe mode. Once on Safe Mode try to perform the action you were trying to do and check if it now works. You should delete the following folders if present: C:\Program Files\Mozilla Firefox C:\ProgramData\Mozilla Firefox C:\ProgramData\Mozilla C:\Users\username\AppData\Local\Mozilla C:\Users\username\AppData\Local\Mozilla Firefox C:\Users\username\AppData\Roaming\Mozilla C:\Users\username\AppData\Roaming\Mozilla Firefox Also cleanup your temporary and rubbish files with Windows built-in hard disk cleaner or alternatives such as CCleaner or TuneUP utilities. *https://support.mozilla.org/en-US/questions/937103