Tab Badge v1.0.2resigned1
Shows a small badge with the unread count (the number between parentheses in the page's title) of the tabs over their favicon.
The only way to do this is to draw a new favicon with the badge over it. Since the icon is only 16x16 pixels, the badge must be relatively small. You can change the font size in the addon options page.
Note: If you find any issue please report it here instead of the reviews section.