I don't believe there is a preference to change this. I found this add-on that does this along with hiding the names of the folders - https://addons.mozilla.org/en-US/firefox/addon/smartest-bookmarks-bar

You might find a more suitable add-on here - https://addons.mozilla.org/en-US/firefox/search/?q=bookmarks&appver=11.0&platform=mac

Thank you for your response though the add-on you suggested didn't do the trick.

Add code to userChrome.css below the default @namespace line.

• http://kb.mozillazine.org/userChrome.css

The customization files userChrome.css (interface) and userContent.css (websites) are located in the chrome folder in the user profile folder.

• http://kb.mozillazine.org/Editing_configuration

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); /* only needed once */

#personal-bookmarks .bookmark-item[container] > .toolbarbutton-menu-dropmarker { display:none!important; }

Ff 11 for OS X doesn't have a chrome folder - they are gradually abandoning the concept at Mozilla.

You do not have a chrome folder in the Firefox Profile Folder by default because the folder is empty, so you need to create a chrome folder yourself if you want to use userChrome.css and userContent.css.