Username or EmailPassword
Number is simply nice. Every one know downloads doesnt equals to user. Users may be more or less! In company like us we download only once and use the same download with 42 people! We are all Linux users. Also most of the new linux dstros include latest version of firefox so those people dont download Firefox.
It will be interesting to see how many users switched from IE to firefox or Opera to Firefox on Windows platform. Linux users have very limited choice between brosers [ Netscape | Mozilla | Opera | Firefox ]