This Recreates the basic functionality of the popular Roomy Bookmarks Toolbar add-on for firefox. It hides bookmarks bar items label text, and shows them on hover.
place the userChrome.css file in C:\Users\your username\AppData\Roaming\Mozilla\Firefox\Profiles\whatever your profile is named.default\chrome. if you dont have a chrome folder you have to make one.
In Firefox 69+ you need to go into about:config and change toolkit.legacyUserProfileCustomizations.stylesheets to true