Since Firefox updated, when I try to click on a link in my Outlook email, I get the error message, A copy of Firefox is already open. Only one copy of Firefox c
I'm on a Mac desktop.
First try restarting your computer - that's the easiest way to get everything Firefox to close.
If that doesn't work, resetting Firefox should do the trick. Instructions and details are here - Refresh Firefox - reset add-ons and settings
You may be having problems in shutting down Firefox properly for some reason.
What is the exact message you receive ?
You may need to look for and kill any Firefox or plugin container processes that are still running. See "Firefox is already running but is not responding" error - How to fix
If the problem continues a screen shot of the message may help