Yup, been using it for ~1 month now. Had the previous one too 3.0.x. It's a slightly different interface than IE but the key for me was that most of the bad stuff is written for IE.... not Firefox (... yet).
Firefox since it was created and Netscape before that. Works on many different OSes like Linux, OS/2, and others. Share a common folder or network to a common folder to all mozilla flavors of firefox and thunderbird.
I found FF 3.5 to be MUCH faster than the 3.0x flavors in rendering pages, but be careful when you upgrade if you are an existing FF power user as a lot of add ons and themes are not working for 3.5 yet
All of the extensions I used have worked fine for updating to 3.5 except the one for Foxcast weather. I had such and old version that I seen a new number version one and it works again. Removed the one that was installed and then installed the newest release. But had to reset it all up. plus had to remove and reselect some of the RSS Live Bookmarks.