Fix for “Close Firefox: A copy of Firefox is already open.” error
“Close Firefox – A copy of Firefox is already open. Only one copy of Firefox can be open at a time.”
You may have gotten this message if Firefox has recently crashed or you killed the process. The reason this error is appearing is likely because there is a lock file on your Firefox profile.
The easiest fix to resolve this “Close Firefox” error message is to remove the lock file from your profile, here is how to do this:
* Open the Terminal, you will need to navigate to your FireFox profile directory:
cd ~/Library/Application\ Support/Firefox/Profiles/
Now there will be a randomly generated name in here attached with a .default extension, like aioruajc.default or groeakc.default, once you’re in the Firefox Profiles directory you can find out what the randomly generated name is by typing:
then type the cd command with whatever the random .default directory name is:
Once inside the .default Profiles directory, you can remove the lock file:
rm -rf .parentlock
You should now be able to relaunch Firefox without the error message.
Note: an alternate method to get to the proper Firefox Profiles directory is to type the following command:
cd ~/Library/Application\ Support/Firefox/Profiles/*.default
The * is a wildcard and will enter whatever directory ends with .default, this only works if you are using a single Firefox profile though. You can then remove the .parentlock file and relaunch Firefox as usual.