Thought I would just post some quick thoughts on the new Firefox 4. I installed it today on my Macbook Pro i7 in OS X (10.6.7). I made sure I didn't write over my Firefox 3 install. It was a lot of fiddling to install all my addons. My first impressions are that it's definitely snappier. However, I ran into a couple of very serious problems within minutes that make Firefox 4 a nonstarter for now for serious Mac users.