"Vanilla Mozilla" -- wasn't that a Hanna-Barbera cartoon in the mid '60s?

You're right: Firefox is the standalone browser subset of the full blown Mozilla package. To be honest, the name grabbed me (I tend to be drawn to things named "Fox", unless they're owned by Rupert Murdoch). And when I first heard of it, all I wanted was a browser alternative to IE, not a full package. I didn't use POP3 email then ... and now that I do, I use the standalone email subset of Mozilla called Thunderbird.

Why not now go for the full package? I dunno... except that I have what I need, and with cooler logos than the T-Rex head. And I have only what I need, without a lot of extra crap some corporate marketing department insists I must have. And I retain the option of running the browser without running the email ... sometimes I can go for hours without wanting to know what's arrived in my inbox.

And: the open-source improvements, extensions (i.e., plug-ins) and themes for each are authored by fellow users of the individual packages, in parallel development efforts. We don't have to wait for something to "trickle down" from Mozilla.