Firefox 3.7 adds per-tab taskbar thumbnails (like IE8) on Windows 7
Now the latest trunk build includes support for per-tab thumbnail previews just like Internet Explorer 8. And just like IE8, the magic works across multiple instances. If you have two Minefield windows open at the same time, you'll get previews for both.
On my 1280x800 laptop screen, I can fit as many as ten previews with the taskbar docked at the bottom or seven on the left where I normally park it. With more tabs open, you'll list view with favicons (again like IE8).
Not a fan of the thumbnails? They're easy enough to shut off. Just head to about:config and search for taskbar.previews. You'll see options to set the maximum number to display as well as the true/false toggle for browser.taskbar.previews.enable. Double click that value, and the change is instant - just keep your eyes on the taskbar icon.
Personally, I enjoy the feature for tab management. It's handy to be able to close tabs without first activating them in Firefox.
To take the new build for a spin, head over to the Firefox nightlies and download the installer.