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Firefox is already running but is not responding error message

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  • 1 has this problem
  • Last reply by cor-el

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Hi. This message "Firefox is already running, but is not responding. The old Firefox process must be closed to open a new window." is recurrent. It happened before, I don't remember exactly when, then stopped when a new version was installed. With the last version of Firefox, it returned. I tried all the suggestions available, namely the one in "support.mozilla.org", but with no success. I guess that this is related with something related with the new version, but it is only a guess. I have a laptop running Win 10, with a single installation. This error occurs essentially when I try to open links from Thunderbird (version, 68.9.0), but there are exceptions. A very few links open in Firefox without the error message. Any suggestions how to fix this issue? Thanks in advance.

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Do you get this message when you try to open a link in Firefox via an external application?

Check the target field in the Firefox desktop shortcut and make sure you do not start Firefox with the -no-remote switch or have set the environment variable MOZ_NO_REMOTE present

  • Control Panel -> System -> Advanced -> Environment variables

If you have a MOZ_NO_REMOTE environment variable then remove this variable and do not change its value to 0 because that doesn't work (Firefox checks for its existence and not the value).