For those of us with lots of tabs (e.g. more than a dozen), favicons are the only way to know what is in each tab. With only a letter or two showing, favicons are the only tab content identifier that exists.
However, my favorites/bookmarks bar is a row of favicons. I feel like The first Macs and Apple IIc did a great job labeling hardware ports with good icons. You could quickly understand what they meant, and worked better than words for the labels. I don't understand why Apple has decided that favicons are such an abomination that using them for tiny buttons in the favorites bar isn't even an option hidden somewhere in a plist.
Really, I just miss having favicons enough, that the advantages of Safari aren't enough to get me using it instead of Firefox.