Firefox does not start. I tried to install Firefox 5 on a Windows 7, 64 bit system. The old 3.6 did very well, but the Mozilla site strongly recommended upgrading to 5.0. But the installation did not work. I was asked to fill in my username and password, although my PC does not have a username or password. I choose 'present user', and then the installation shutted down. Then I gave my computer a username and password, but still nothing happened. Well, back to 3.6, but that also failed! What happened?