I've downloaded the browser bundle, created a new folder in applications and moved it across from downloads to there. I've even moved it to the desktop and tried opening it. I've rebooted my Mac 3 times now too, after closing all programmes down. It still says Firefox is already open, and the application keeps attempting to open 2 Tor browsers, just before it gives me the "can't open because Firefox is already open" message. I don't have Firefox on my machine.
Any advice? I'm thinking I might bin it and try again? I somehow doubt that'll fix the problem though. There's obviously an issue with it running. I've looked through the answers to the same question, nothing is working and some of the advice is for Windows machines. Thanks in advance!