The taskbar previews for tabs brings Firefox into parity with Internet Explorer 8, allowing users to see and select their open tabs via Aero Peek. The obvious limitation with this feature is how it impacts the display when you've got a high number of tabs open. As you open more tabs, their preview panes will shrink.
While the taskbar preview will work without manually changing settings in about:config, the others will require a bit of fiddling. As such, they're not recommended for new users, or for those who just aren't comfortable tweaking the about:config.
The enhanced Control + Tab will now show you a preview window of your tabs, as long as you have three or more tabs open. To activate it, go to about:config, search for browser.ctrlTab.previews, and double-click on it to change it from False to True. Then restart Firefox, and the CTRL+Tab hot key will give you Aero-style preview pane of your tabs.
A revision to the List All Tabs feature gives it a visual component mimicking CTRL+Tab. Using Control + Shift + Tab combo, you can pull up a CTRL+Tab tab preview window that includes a search box. As you type in the name of the tab you want to call up, it will filter the tabs. Enter or the left mouse button will take you directly to the tab. To activate this one, go to about:config, search for browser.allTab.previews, and double-click on it to change it from False to True. Then restart Firefox.
You can disable the Windows 7 taskbar preview by going to about:config, search for browser.taskbar.previews.enable, and double-click on it to change it from True to False.
As this is a beta, be prepared for Firefox to break compatibility with many add-ons. In my test, All-in-One Sidebar wasn't compatible, even after doing the stability-reducing version compatibility override. Also notice that the visual component to the tabs previews within Firefox don't appear to be fully baked.