Bookmark bar is a panel with links which is always on top of html document, if the user wants to see it. It is handy for some scripts which modify something on webpage. I know 2 of them: Reveal Bullshit [1] and how to make youtube speed 3x [2]. Do you know any other examples worth of mentioning?[1] https://mourner.github.io/bullshit.js/
[2] https://stackoverflow.com/questions/30521498/how-do-i-change-the-playback-speed-of-the-currently-playing-youtube-video-with