This one has been a long time coming, I just keep forgetting to put it up.
It is about 95% love and 5% hate, but the reasons that I hate it are very profound.
Firefox is awesome. I can't really remember when I started using it, but it was several years ago. It is awesome since it displays my sites correctly (although under Ubuntu some sites look weird, I think the fonts are bigger or something in the Linux version of Firefox). It is awesome because of all the many extensions like Firebug, Greasemonkey and HTML validators that make my life as a web programmer so much easier. I can use tabbed browsing (although the novelty of this has faded over the years, especially since any modern browser does it too) and have my little RSS feeds in the links bar. And finally it is awesome because I can browse porn sites or the other red-light districts of the Internet without fear of dialers or other nasty bits installing themselves on my system, although this has really no relevance anymore now that I mainly use Ubuntu for everything.
So why does it suck? Mainly because it uses up a ridiculous amount of memory. I have the little RAM gauge on a GNOME panel, and when I close Firefox, it really drops. Oh, system's getting slow? Restart Firefox. How can a browser suck up so much memory? It is ridiculous!