firefox is already running, but is not responding. To open a new window, you must first close the existing Firefox process, or restart your system

"Firefox is already running, but is not responding. To open a new window, you must first close the existing Firefox process, or restart your system"

WARNING My fix on this post is a quick fix to get you back up and running. It does NOT fix Firefox and save all data (bookmarks, histroy etc.) it only gets Firefox back into a running state.

1. Right-click on the Firefox icon
2. Properties
3. In the "Target:" field , scroll all the way to the right after the address
4. Add -profilemanager after the "
5. e.g. you should have something like this now "C:\Program Files\Mozilla Firefox\firefox.exe" -profilemanager
6. OK out of everything
7. Run Firefox
8. Make a new profile or delete the old one and make a new one
9. Remove the -profilemanager
10. Run Firefox as normal