One of the new features in Firefox 3 will be tab preview. This feature will show you thumbnails of currently opened tabs.
First, the List all tabs button in the tab bar is replaced with a button that opens a black window with thumbnails and the active tab highlighted in a slightly bigger size. Tabs can be located by inspection or you can enter a few letters from the tab title you want and thumbnails are quickly filtered out.
Switching tabs with the Ctrl + Tab (Cmd + Tab on Mac) brings a black bar across the whole screen with thumbnails of the closest tabs with the site’s favicon overlayed for easier identification.