With vertical tabs you can make the tab list as wide as you want, and thus can fit the favicon plus portions (if not all) of the document title. In addition, if implemented with some thought, you could have new tabs nest under their parent tab.
Enter Tree Style Tab for Firefox. It’s an add-on that does all of the things mentioned above, plus it lets you choose whether you want the list on the right or left, amongst 100+ other options (seriously).
Looks great, I'll give it a try.
Just make sure you have the 'Title Bar' enabled in your 'Customize' options. Otherwise disabling the integrated tab bar via CSS you disable the window decorations (close button etc.) as well, which turns out to be quite annoying.Link