I also fiddled with Firefox. I haven't enough time to really test them out, but here are my initial impressions.
The One-click site info sounds more interesting than it is. Most sites, including Mozilla's own, don't have any identify information. However, if you go on to the advanced tab, it will show you whether the site has placed any cookies with your Web browser and can show you detailed information on what's what with those cookies. This strikes me as being darn useful at times.
The malware and cross-script-aka Web forgery protection-protection mechanisms do work. Neither feature offer perfect protection, nothing does, but anything that increases Web security is a good thing in my book.
As someone who makes more than his fair share of typos with passwords, I'm pleased to report that Firefox now only asks if you want to save your password after you successfully logged in to a system. Maybe this won't matter to a lot of people, but for me it gets a big thumbs up.
I suspect more people will appreciate the improvement in bookmarking. For example, the new Smart Bookmarks Folder lets you quickly go to your most often visited pages from the smart bookmarks tab on your bookmark toolbar. Firefox 3 also enables you to add keyword tags to your bookmarks and then sort your bookmarks by these tags. I'm not a big fan of tagging, but for those who can't live without them, it's extremely handy.
All-in-all, Firefox 3 is more than good enough to keep me as a user. Better still, from Mozilla's viewpoint, its good enough that it should pull in another wave of new users. It's not just a major step up from Firefox 2; it's a leap forward from the other new browsers such as the forthcoming Internet Explorer 8.