Some while ago, I submitted a bug to the Gentoo Bug-trac. I had trouble with Firefox 2.0.0.2 when switching from non-proxy to a proxy-network.
http://bugs.gentoo.org/show_bug.cgi?id=169155
I found that when starting firefox (note: not firefox-bin) the proces wants to connect to www.gentoo.org 
Now someone found the issue:
I have the same problem with mozilla-firefox-2.0.0.13.
Firefox tries to connect to the page mentioned in
/usr/lib/mozilla-firefox/defaults/pref/all-gentoo.js:
pref("browser.startup.homepage", "http://www.gentoo.org/");
If DNS or the page itself is unreachable firefox waits until the request
timeouts.
I haven't test it yet... but it might solve the issue... 
