Sorry, Ebbie...I assume too much... A "file manager" is a generic term for stuff like "Windows Explorer" which I 'almost' never use, since there are better ones. It just lets you look at all the files on the computer. Once you get used to what to look for, you may see patterns...including bad ones.

Jeri's idea is the right one, but I can't imagine why none of the standard tricks aren't working. If Firefox IS 'open', it should show in 'processes' under ctrl-alt-delete.