Steve, Firefox 1.5 has been cooking for some time (I read about it a lot because I read news sites that talk about it). It's the path to 2.0

As for Mozilla 1.7.12, Jayson, just like Marie said, Mozilla and Firefox are completely separate programs. Mozilla is the old "Mozilla Suite", which includes a browser, an e- mail client, a webpage composer and a chat client (if I recall correctly) all in one program (which is actually several different programs but nevermind

).
Firefox and
Thunderbird are the "new generation" of browser and e-mail client from the Mozilla Foundation. They are intended to replace the Mozilla Suite sometime in the future.
Judging by the download numbers, Firefox was a huge success when 1.0 lauched.
In just 4 days, the 1.0 preview release counted more than 1 million downloads; in the very same day the 1.0 final version was launched,
the download count for that day alone was way above the 1 million mark; 32 days after 1.0 final was released,
10.000.000 (yes, ten million!) downloads were registered! And it's still slowly taking market away from Internet Explorer.
Besides, not every browser can brag about having a
two page ad in the New York Times!

Taking into account that this is an Open Source project, I think it's quite a feat

I've been using it since its 0.6 days and all I can say is: give it a try. Actually, give them both (Firefox and Thunderbird) a try!

By the way, for those of you who already knew mozilla.org, Firefox and Thunderbird are now hosted on a new website, mozilla.com