Contrary to most (at least, that's the impression I get), I am extremely anal about my web browsing habits - if I'm not using a page, it goes down. I find it pointless to open dozens of tabs while you can only stare at one at a time anyway. Right now, I have only the tabs open required for this particular story - and a tab for Facebook that I can barely manage to not compulsively close.
I've seen screenshots of some of your browser windows over the years, and I'm often surprised by how many tabs people have open. Well, this new Firefox trick, called Panorama, should really be of help to you since it makes it easier to group tabs together in a natural fashion. It is vaguely similar to Mac OS X's Exposé, with the additional ability to create your own visual representation of groups of tabs.
I've played around with the new feature on Windows 7, but I was less than impressed. I found the animations to be choppy, the miniatures representing open tabs were pixelated, and basic things like resizing the Firefox window reminded me of Windows XP's visual wear & tear days of animations. It's still a beta, of course, but I'm just baffled as to why it's so hard to get even these basic things right, and it doesn't inspire confidence in the rest of Firefox 4.0 at this point.
But alas, I'm probably not the right person to talk about Firefox ("if the browser is not Chrome, then it sucks" is my motto). How are you actual Firefox users experiencing the Firefox 4.0 betas?