I went to FF3 last week. I use very few extensions on my "work" machines, because I'm testing cross-browser compatibility and most of my users don't have extensions, so I need to see what they see. (Yes, I know most extensions shouldn't affect the CSS, but sometimes I really need to see what they see-- no extra features.) I have XRAY and Firebug installed, and DownThemAll. But I might add some new add-ons based on what people have been suggesting here. (What's this about being able to emulate IE rendering in FF?)
Unfortunately, to my great surprise and disappointment, FF3 actually broke on some of my CSS that was working on FF2, IE6 and IE7. It's a div width thing, not fatal, but ugly. I'm actually kinda mediocre with CSS-- just haven't had enough practice yet, and nearly everything I know is from fiddling with style sheets that come with software I'm using, rather than starting from scratch. I expect I'll figure it out eventually. But I was surprised to see something break on FF3 that was working in FF2.
