Debian Jessie and Firefox and Gnome may sound like an odd threesome, but Jessie can run Firefox as a native Gnome 3 application. And why would you want to do that? Debian already comes with a perfectly good web browser — Iceweasel, a rebranded version of Firefox. Why? Because of updates. Firefox updates much more often than Iceweasel. If you want the latest features and the latest bug fixes and security updates, you want Firefox.