If Firefox did not shut down normally when you last used it, Firefox might still be running in the background, even though it is not visible.
End Firefox processes
Use the Windows Task Manager to close the existing Firefox process:
- Right-click on an empty spot in the Windows task bar and select Task Manager (or press Ctrl+Shift+Esc).
- When the Windows Task Manager opens, select the Processes tab.
- Select the entry for firefox.exe (press F on the keyboard to find it) and click End Process.
- Click Yes in the “Task Manager Warning” dialog that appears.
- Repeat the above steps to end any additional firefox.exe processes, if more than one entry is found, then exit the Windows Task Manager.
- Start Firefox normally.