Firefox has had 10 million downloads so far from the official site. That does not include copies distributed by individuals such as myself and those included in other projects such as the OpenCD and various Linux distirbutions, so the actual number of users should be somewhat higher.
My browsers:Firefox on the #1 Machine.
Mozilla on #2 but is almost never used for browsing.
Mozilla on #3 Machine.
E-Mail - Thunderbird.
I mainly keep the Mozilla around to edit my local homepage with all my links and E-Mail addresses on it.
The Open CD is a useful location for open source software for windows machines. Version 2 just released. Includes Firefox and Thunderbird.