Great tip on Lifehacker for how to add favicons to the bookmarks toolbar in Firefox 3 for Mac OS X.
One of few things I do not like in Mac versions of Firefox is the fact that there is no favicons on the bookmarks toolbar. I am a visual person, so having favicons on the bookmark toolbar really helps me pick out bookmarks quickly. This resolves that issue.
If your interested in voting for the bug in Bugzilla regarding this, the bug # is 348719.