Well, where do I start?
Firstly, as mentioned before by many other reviewers/bloggers, FireFox is amazingly fast at rendering pages. And, tests by Adrian over at ZDNet show that FireFox is faster than any other browser out there. So, to summarise this point – its damn fast!
Secondly, there has been a graphical user inter’face-lift’ which is quite appreciated. Obviously, this will not prevent people from making their own themes, and using the ones that can be found on the addons site, but its a nice change.
Thirdly, the configurations that can be made in the ‘Tools>Options’ sections have stayed the same on the most part but a few little tid-bits have been added in to give more control to advanced users.
Fourthly, the way that FireFox has made ’search’ & ‘favourites’ such a big part of the browser as a whole is a big PLUS as it makes it a whole lot easier to navigate and keep hold of the sites you want to visit frequently or to just bookmark [no pun intended].
Fifthly, and this is a carry on from the ’search’, that the way all your pages that you have visited are indexed so that as soon as you type any letter/word into the URL bar, it picks up on any main words in the pages you have visited before. This is really good, its almost as if Spotlight from Apple is integrated straight in.
Lastly, and this is one of the flaws, that rendering on some sites such as DeviantArt isn’t working properly and I think this is to do with the ‘JavaScripting’ on pages. I have also encountered this issue with some other web pages but since it still ist RTM, I can’t really complain.
Also, for all thos people who rely heavily on addons and extentions for FireFox, I would wait until the official RTM release is out seeing as developers havent yet finished making their addons native to FireFox 3.
Overall – a killer browser, but for those who like the Mac style on Windows, Safari 3.1.1 isnt far off and came second in rendering speed 
Hope that helps =)
