Anyone who has anything nice to say about Mozilla's Firefox browser has such because of emotional bigotry, not objective analysis. I have been running Firefox on both Linux (SuSE's latest) and Windows (XP Pro SP2) since beta days. With each release and each patch, I expect the uncountable list of problems to abate. Instead, the list grows only longer.
On Windows, Firefox has plenty of plug-ins, though not enough. It freezes constantly. It is unable to interprest RSS or RSS2 from most sites where other browsers, including the crappy Opera, have no trouble.
On Linux, Firefox is even worse. It is hideously slow and has very few plug-ins. Those it does support--RealPlayer, for example--do not work as expected.
For usability, though, IE is still champion. (In case you're wondering, until I can afford dual P4 3.0 ghz processors, I will not install Netscape, perhaps the worst commercially produced software ever written.) IE is fast, it has intelligent and configurable caching, and allows developers to do the things users demand. Its security problems are exclusively the result of its popularity.
Firefox 1.0 had numerous, serious security holes. I can only assume that the rest of the application is so awful as to prevent its popularity from making it a target for hackers. Unless a 2.0 version comes that actually works, Firefox's developers need not worry about that scenario.
Update: Here's Firefox lover who has started a blog about problems with Firefox.