I’ve installed all of the major browsers on several of my machines in order to make sure that MO works correctly regardless of what flavor you browse with. (For instance, Firefox apparently cares whether I close my [small] tags at the end of an update…)
I probably do about a third of my browsing with Firefox. I also use Opera from time to time. I rarely use Netscape, which is built on Mozilla technology, though I do like their little “New Tab” button.
In response to the buzz that Firefox has been generating of late, maybe MS should hire the former Iraqi Information Minister to deal with the PR aspect of the issue. Something along the lines of “The Firefox infidels are committing suicide by the hundreds on the gates of Redmond. Be assured, Internet Explorer is safe, protected.”
FWIW, I still do most of my browsing with IE and will probably continue to do so.