In case it helps any:
What camorri wrote about the home page setting should be correct. But if that's not working (for some weird reason?) check in your about
:config page (enter
about:config into the address bar) and in the search bar there, type the word
home. This should produce a dozen or so items.
See that you have an entry:
browser.startup.homepage
That's the one that's tied to the
Prefs -> General -> Homepage setting. If it's empty, something else gets used instead (see below):
If that's empty, I believe one of
startup.homepage_welcome_url or
browser.startup.homepage_override.mstone takes over, but I could definitely be wrong about these.
FWIW I am currently using FF 3.6.10 also, but my home button works fine (though I don't actually have it on my GUI as I don't use it).