I try to do as much as possible from my keyboard using shortcuts, because I think it's more efficient than using a mouse. As such, I frequently employ the Safari (and Camino, not sure about Firefox) keyboard shortcut Command-(1 through 9) that triggers your Bookmark Bar bookmarks. The problem is this actually slows me down because I can never tell at a quick glance whether a particular bookmark is Command-4 versus Command-5, or Command-6 versus Command-7, etc.
Here's the fix: in the Mac OS Character Palette (under the International icon in your menu bar), select the All Characters view from the View drop-down. Select the by Category tab, and then under the Symbols section in the left frame, select Numbers and Number Symbols. Scroll about two-thirds of the way down and look for the rows of seemingly-normal number characters right below the fractions. The first row of 0-9 are actually superscript characters, and the second row are subscript (I prefer subscript, but either will work):

Mac OS X Hints
http://hints.macworld.com/article.php?story=20070706204140804