Maybe you do not have internet connection before you load firefox.
I have broadband internet which is always on, but sometimes my computer's loading and I have to wait a minute or two for the computer to establish internet connection. If I load firefox before and it loads just before the internet connection is available, then it'll say server connection problem error. (server can't be found or something like that to my homepage).
But once my internet goes online, I can surf to any website that's working ... even google and my own homepage that I already set as default.
If that is not the case for you, maybe it's a problem with google.