Strange, I am on the same version (OS X).
I ran into a Firefox peculiarity the other day. I was trying to configure a CenturyLink (ActionTec) modem/router and it wouldn't save the settings. When I tried it with Safari, no problem. I've seen a few other things which Firefox wouldn't handle correctly but a different browser would deal with just fine.
I had something similar on my Actiontec router using Firefox and WIndows Vista. But it was everytime I clicked on DHCP reservations, I would lose internet connectivty from the router. Literally, the light for "Internet" on my router would go off every time I clicked on DHCP reservations.