Blacklist Firefox 13 and 14 too

Firefox 13 and 14 were the cause of links magically turning into [[./Foo]].
Once the immediate rush of deployment is over, we'll want to investigate as
to why and hopefully find a way to unblacklist FF.

Bug: 50720
Change-Id: I7a9dddb693091fa1e44b4325e77b9e4f55e5c193