Find which Firefox profile is being used

Firefox allows users to have different profiles when starting the app. To figure out which one you're using, type about:cache in the browser URL field.

Look for the Storage disk location entries, it'll be something like /Users/example/Library/Caches/Firefox/Profiles/8686feh.FF43/cache2

The part after the weird string (8686feh in the above example) is the profile being used.