Can’t open links in Firefox on Ubuntu when it’s open – Fixed!
This is a little obscure but there’s a number of people with this problem and too many “simple” answers that just don’t work. There are a number of situations that cause Firefox to respond with an error message when you click on a link from outside of the browser (like Thunderbird or any other application that try to launch a url). You get an error message saying:
Firefox is already running, but is not responding. To open a new window, you must first close the existing Firefox process, or restart your system
The normal reasons for this are things like locked profiles etc. which are well covered here. But some users get this error message even when Firefox is open and there aren’t locked profiles 😦 The solution is to edit the way that Ubuntu invokes Firefox.
Grab a terminal and go to ~/.local/share/applications this is Unity stores it’s information for launchers in the unity dock thingy. You should have a Firefox.desktop in here, you might have several in which case the one called “Firefox Web Browser.desktop” is probably the one that Ubuntu is using by default.
Edit the file and have a look at the “Exec=” line about 4 lines down. In my case the problem was caused because this line was referring to an old profile that I’d previously removed trying to fix the problem. If you’re not sure what it should look like set it to “Exec=firefox %u“, save, exit and click links once more 🙂