Hi DanT, did you already have this set up for older versions of Firefox and your userChrome.css rules stopped working? You can find updated rules here: https://github.com/MrOtherGuy/firefox-csshacks/blob/master/chrome/multi-row_bookmarks.css ''If that didn't make any sense to you:'' Add-ons are not able to make structural modifications to Firefox's toolbar area, but you can accomplish that using style rules in a an optional userChrome.css file. More information on userChrome.css here: https://www.userchrome.org/