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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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Alex George
Alex George has Engineering graduation in Computer Science and an MBA in Finance. He had been working as a senior Network Engineer for ten years. His specialization is in Cisco products. Traveling is one of his hobbies and visited various places as part of his onsite work. He visited different places as part of his onsite work like New York, Dubai, London, etc. Right now Alex is a director of one of the leading career development firms in India, which trains students for UPSC, SSC, and PSC examinations. He guides a lot of students to get selection for various prestigious institutions like CBI, Income Tax Department, etc. Alex George is a stock market investor and a very active intraday trader. Engineering Background: He has a B.Tech in Computer Science and Engineering and passed different network and security courses like CCNA, CCNP (Security), CEH, and various Microsoft certifications. Finance Background: Alex has an MBA in Finance. He is an active intraday trader and a Share Market Investor. Webmaster Skills: Alex is a blogger since 2004. He has a working knowledge of HTML, CSS, PHP, and JavaScrip.