Mozilla has ended or is ending (Mozilla issued one current update for Firefox 48) support their browser on OS X Snow Leopard through OS X 10.8 Mountain Lion
It will end with some last version of FF 48.
You can update to the latest FF 48 version and install the latest Adobe Flash Player.
OR
Do a search for Mozilla's Firefox ESR program. It is a slightly older version of FF (FF 45.x) and is a security update version only of FF.
Disregard all of the enterprise and educational institutional stuff.
You can download, install and run the Firefox ESR versions.
You can still use the latest Adobe Flash Player, but Mozilla is not offering anymore feature updates for FF users still on 10.6-10.8.
Only security updates until April 2017.
Your only other option for a web browser that is still supported for OS X 10.6-10.8 and later is SeaMonkey.
Do a search for the
SeaMonkey project
I don't have any links handy.
Good Luck!