Nevertheless, one of the things that's always irked me about the Mac version of Firefox is its lack of favicons in the bookmarks bar right out of the box. Pouring salt on the wound, no amount of research through Firefox's help files, Mozilla's forums or even Firefox's own config file (accessible by typing about:config in the address bar) yielded any kind of explanation or workaround. But thankfully, I finally found a solution, so if you're in this same bucket and you want favicons in your Firefox bookmarks bar, listen up: it's all (apparently) about the theme. I don't know how or what exactly these theme authors are doing, but installing some of the themes available from Mozilla's add-ons site will bring favicons to Firefox's toolbar once you enable the theme and restart the browser. I first tried the Blue Ice theme which worked just fine, but finally settled on Mac Favicon which simply edits the default theme to enable the tiny but handy icons. I'm sure more of the themes at Mozilla's site will do the trick, and I would bet that checking their preview screenshots to see if favicons are indeed visible should save you some time when searching for the right solution.
I would imagine Mozilla turned off favicons by default to make the browser look and feel a little more like Safari, but they could have made our lives easier by simply offering a menu item, possibly under View. Ultimately, an add-on like the ones I've mentioned are a decent enough solution for now, but I recommend you submit this as feedback to the Firefox team if you've been jonesing for favicons as bad as I have.