You might want to check for updated packages. Or upgrade your Mint install; if so, this might help: https://gist.github.com/hgomez/7074150

If you install via a package manager on Linux then generally you can only update the browser through the package manager. On my Gentoo box that's how I have to upgrade chromium and firefox.

generally distros do that yes. because they ship updates through their own package manager (in this case apt) instead

if you get firefox directly from mozilla you'll have mozilla autoupdates.

in general, both are fine..