You can adjust the font-size for specific elements via code in userChrome.css, but you will have to be more precise for what cases you want to make this change. Is this only about bookmarks and folders and its content on the Bookmarks Toolbar or also about other places where you can inspect the bookmarks ? Can you attach a screenshot? *https://support.mozilla.org/en-US/kb/how-do-i-create-screenshot-my-problem *use a compressed image type like PNG or JPG to save the screenshot