I cannot say what I found in Firefox 4 aren't cool enough but they're awesome. Because of those, I cannot write that much coding for my projects when I push my clients to use Firefox 4 as our project default browser. Don't look at those new changelogs first. Just look GUI of Firefox4. I can feel it's cool because they can screw the layout of menu toolbar and the obvious button for previous browsing history. Another one is saving password. I can obviously see the message box after I typing password into my blog, email or etc.
Ok, here is one of my changelogs of Firefox4 for me.