The Web Developer extension adds various web developer tools to the browser.
IE Tab - an extension from Taiwan, features: Embedding Internet Explorer in tabs of Mozilla/Firefox...
TabGroups Manager helps to classify and organize tabs by dividing them into Groups. Because tabs become easier to manage, you can never have too many! TabGroups Manager is ideal for tab power users.
Change your bookmark icons! Right-click a bookmark, and select "Properties", then "Browse" for a new image or paste in a URL.