Ever since Firebug got a recent big upgrade, I've had problems with it stopping a page from loading whenever there is any javascript error. Since the web is riddled with javascript errors, this has meant a frustrating experience. It used to be easy to turn this behavior off, in the Script tab, but now there seemed to be no way to stop it from stopping.

I'm still not sure of the cause, but this little fix seems to have corrected the problem:

From the Firebug menu, select Options > Reset all