So now we have Firefox 2 as well as IE 7, and (presumably) a whole new set of incompatibilities to work around before web pages work in those and the earlier browsers.
My initial impression is that it’s as quick and good as ever it was but I’ve not noticed anything that’s really going to improve my quality of life to any great degree. Personally I don’t like the close button on each tab and preferred having just one. There doesn’t seem to be an option to use that system, either. Anyway, it’s still going to be my main browser.
[UPDATE]: You can go back to the old behaviour by visiting your about:config page and changing the value for browser.tabs.closeButtons to 3.