Firefox is already running, but is not responding

Ever since upgrading to Firefox 25 I have been getting this error message randomly when starting a new instance of the browser:


Apparently, Firefox hadn’t shut down properly the last time I exited it, as I could still see the old process hanging around.

Originally, I had figured I would wait, maybe there was a fix under way. But since a few weeks have passed since the update, and we are now on version 25.0.1 already, I figured there was no point waiting anymore. So instead of starting Firefox directly, I now use this small batch file:

taskkill /IM firefox.exe /T /F
start "" "C:\Program Files (x86)\Mozilla Firefox\firefox.exe" -p default

I saved it as a cmd-file and redirected the pinned shortcut I had previously used to start Firefox directly, to point to this batch file instead.

To do that, just

  • Copy the path to the batch file (e.g. by right-clicking the file while holding down the Shift key) and clicking Copy as path)
  • Right-click the pinned icon,
  • In the menu that opens up, right-click Mozilla Firefox again,
  • Click Properties, and
  • In the properties dialog, paste the path into the Target text box.


Now, the batch file kills any existing instance of Firefox before starting a new one. Unfortunately, this does not help when opening links from other applications such as your email program.

Hence I’m still interested in fixing this problem for good. If anybody knows how to do that, please leave a comment.

[2013-12-21 Update] I was upgraded to Firefox 26 yesterday and I haven’t had the problem since.

[2015-02-18 Update] Even with Firefox 26 and newer the problem appeared sometimes, though far less frequently. But since the dialog was redesigned to allow killing the unresponsive Firefox instance, this isn’t really an issue anymore and the above workaround is no longer needed.