Another Instance of Firefox is Already Running

Yesterday I faced a strange issue on my computer. I was unable to close the Firefox browser opened in my computer. I clicked the close button but it was not working. It seems like the program is stuck and not responding. After some time, the browser closed but that was the beginning of another problem. I couldn't open it anymore. I double clicked the shortcut icon but it was not opening and showed an error message saying "another instance of Firefox is already running".

Another Instance of Firefox is Already Running

When I double clicked the shortcut icon, I received the message another instance of Firefox is already running. However, it was not open on my computer at that time. For my PC, this program was already running and there was no way to open another session. In reality, that program was not functioning at all.


Though the browser was not working, its process was active. I confirmed it by task manager and the only option to solve the issue was to close the running process. After terminating the process, I could start the browser without any issues. The procedure to fix this issue is given below.
  • Open Task Manager by pressing [Ctrl] [Alt] and [Del] buttons together

  • Click Process tab

  • Select the Firefox process and kill

After finishing this procedure, you will face no troubles to start Firefox on your PC.

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