Need a bit more info about this situation. What operating system are you running? XP? Vista? something else?
Do you have a firewall running? XP and Vista definitely have one enabled usually by default and they're easy to misconfigure by accidentally hitting "deny" when the dialogue pops up.
The reason that I ask about the firewall first is because secure sites are browsed to on a different port than normal http, so that port may be blocked.
Corey is right about needing to know more information as it could be related to something you've pushed in each browser accidently, something on your network router/modem, or something like a firewall build into your system. Just in case, you may, however, want to try resetting Firefox's cookies, history, etc. by clicking tools, and going down to Clear Private Data. Then check every box and push and click Clear Private Data Now. A word of caution though, this will erase everything, just like it says.