Unfortunately there's no way to attach to a non-IE browser in Visual Studio unless someone knows of a trick I don't. You'll want to either use the infinitely useful Firebug Extension for Firefox or the more feature rich Venkman debugger.
I have had issues with scripts being cached in FF while you're developing, so I would suggest making frequent use of the [CTRL][SHIFT] + Delete shortcut to clear your cache. Another trick I use is to insert
debugger;
into your script where you want to make sure you break into the debugger. I'm sure this works in Firebug and may also in Venkman.
Happy debugging.