I'm currently running Firefox 3.6 (Beta 1), which I downloaded recently today (I think). It's quick, it has handy features and tons of add-ons, that's why.

I don't use Microsoft Internet Explorer simply enough because it sucks. There's one thing that I like about it though, and that's the default search engine - which for once isn't Google. Not that Bing is that great...

I don't use Google Chrome mainly because of the lack of privacy, but it lacks Firefox's number of add-ons as well, and you can't really trust Google...

I don't use other browsers because they lack a wide variety of add-ons (sometimes at all), and many of them are dependent on Google...

If there was one thing I'd want to change in Firefox, then it wouldn't be the design, the speed, the features; it'd be the default search engine, although everyone is free to change it, many people do not.

Firefox fits all my needs, besides the "Google thingy", but I can forgive them for this one. That's also why I use it.