I’ve been running a portable version of Firefox 3.5 b99 (a preview release) to see what the excitement was about. I was a little disappointed. Aside from a few very minor cosmetic changes, it looks the same as 3.0.x.
I didn’t do a formal speed analysis, but it felt like it loaded pages a little faster, especially Google’s AJAX-heavy sites like Google Calendar, Gmail and Google Maps. RAM consumption was about the same as 3.0.x and there aren’t any immediately obvious new features. The majority of the changes are under the hood, as illustrated by this demo given to the Techcrunch folks. The demo has a great wow-factor, but it doesn’t affect my day to day use of Firefox.
After a few days of running 3.5, I’m not inclined to jump onto this release early. The new features aren’t enough to warrant dealing with bugs and instability.