I support as many as possible, right now it is all but Konquerer, Looks like I might be dropping ei6 also(the only person that I know that still uses it, is getting laid off their job). I support, and use Firefox the most. I use several different testers that each test for functionality, and security.
<rant>
If all browsers would adopt W3S standards, it would make it much more coder friendly. If coders would drop support of the one's that didn't, then they would be forced to adopt standards. IE is getting closer.
</rant>