I love it. I've gotten spoiled by being able to run everything in tabs, especially viewing forums. I just load the browser, start at the top and work my way through the sites.
Only issue I've had is lack of spell check support. There is a add-on for a earlier version of Mozilla but it does not work with Firefox and it is buggy - would randomly cause my last version to crash when I ran it, or it would skip words. Spell check should be built in, they say it would cost too much to license a dictionary to do so but I still think it should be.
I love the download manager now, I hated it at first also but I've gotten used to it and have found it handy. With IE on some sites you could only download 2 files at a time without loading another browser session, it's not the case w/ Firefox. I had four 700mb files downloading at once and it was nice to only have one window open showing their status rather than four pop-ups like IE. Also when minimized it shows the total percentage of all files done so have an idea when your bandwidth is going to be free again.
Only site issue I had was with Microsoft.com, you cannot use their download service with Firefox, so when I went to install SP2 I had to go into IE.
