Another answer recommended "Right click on the .torrent file..." or "Firefox go to Edit > Preferences > Applications change default application for magnet"
What do I do if I can't find the .torrent file? Where does my system put these by default (as far as I know I haven't changed the default location)?
When I try to change the Firefox default application for magnet, I just get a file browser. Where do I point it? Where does Ubuntu store my programs, and what are their names? In Windows I'd look in "programs" for an .exe file with the same name as the program I want to use, what do I look for in Ubuntu?