Generally, if you click the browser icon and it doesn't do anything, or gives you an error that mentions profiles, there's probably a previous instance of the browser that didn't clean up after itself. The first thing to check is if you have the browser open on another workstation. If you're logged into two workstations and try to start a browser on both of them, it will cause an error because the application wants to ensure that there is only one copy of it running. We use a network-mounted home drive, which is how we are able to access our files easily on different workstations, but it also means that the browsers will only work on one workstation at a time.
If you are logged in on two machines, exit the browser on one before trying to open it on another.
If you are not logged in on another machine, then a previous session probably didn't clean up after itself when it exited. You'll need to delete the browser's “singleton lock” – the files that the application uses to prevent more than one copy from launching. Open a terminal, and enter the command from the section below, depending on which browser you're trying to launch.
rm ~/.config/BraveSoftware/Brave-Browser/Singleton*
rm ~/.config/google-chrome/Singleton*
Firefox is less likely to do this at all, but harder to fix if it does. First, search for locks:
find ~/.mozilla -name lock
Then delete any files returned by that search. Example:
rm ~/.mozilla/firefox/ly57w6fv.default-release/lock
If you have trouble getting your browser working again, feel free to email tmorris@vassar.edu or swing by my office during work hours