Firefox isn't in the Debian repos, unfortunately. But Iceweasel is installed by default on the desktop, so there's that. Unfortunately, Iceweasel is chronically behind mainline Firefox and suffers from many horrifying bugs that make it almost not worth the effort to try to use, which is why the grandparent comment goes through so much effort (Well, outside of the obviously well planted troll.)

Also, Linux Mint is a terrible way to get Firefox for Debian. You're better off installing it from the "Ubuntuzilla" repo, which contains just Mozilla components built for Debian-based OSes: http://sourceforge.net/projects/ubuntuzilla/ (Ignore the hellhole that Sourceforge has become).

Honestly, I wish Mozilla would just create a Debian repo (and one with Nightlies would be nice), but I understand the scorched earth there...