I'm not a huge fan of Firefox, but I don't think that it is ugly. It does fit in quite well in OS X, and doesn't seem to have odd features that stand out. Firefox handles better under load (like rendering video or Minecraft) than Chrome, and I've ditched Safari a few months ago, because it just simply wasn't getting new features, and started feeling stale.<br /><br />I don't use Firefox as my main browser (I use Chrome), but if I use a web browser, and there are some features that I almost couldn't live without, I'll switch. Personally, if Opera stepped up their game a little bit more, I think I might use that as my default browser, because I like the ease of the folder tabs. Unfortunatly, it doesn't have that nice feel that OS X has (like the new scrollbar integration and a visual "previous page" animation).<br /><br />Pretty much, whatever browser wows me the most is the one that I want to use.