Like most power users, I always have at least Google Reader and Gmail tabs open... and they always take up so much space. If only there was an extension to shrink certain tabs down to just the very memorable icon. Let's take a look at my Firefox window on a normal day...  look how much space the tab buttons are taking. Now look at my browser with the FaviconizeTab extension installed. So much cleaner!

The best thing about this extension is that you can configure it to always shrink down certain tabs, based on the URL.  You can also choose your preference for how to shrink the tab, or just use the right-click "Faviconize" from the menu.

You'll notice that I added in the URL for Google Reader and Gmail into the list. This now a must-have extension for me. If you have a commonly used tab that doesn't have an icon, you can try using the Favicon Picker as well. Download FaviconizeTab from Mozilla Add-ons