I'm running Daryna and i've just installed Firefox 3 through Synaptic.
Just type in the Search Box "Firefox" and it'll just show.
From then on,it's easy to install it.Just click on "apply" and you're done.
MB:MSI 770 C-45 / HD1:500 GB-->Windows / HD2:320 GB-->Mint 17 Cinnamon
CPU:AMD X4 640 3.00 GHz / RAM:4.0 GB / VGA: NVidia GeForce GT630