When you click on "+ Add to" (for adding a new video to a playlist) YouTube displays the playlists -by default- in a strange order: beginning with the one selected last. This script arranges your playlists alphabetically, making it easier for you to find the one you are looking for.
Doesn't work. YT has its own A-Z filter for playlists anyways. But if it's turned off by accident or deleted during a cookie wipe, this script does nothing to sort the lists. By default YT filter is 'recently added', and their filter still manages to override this script! Only setting YT filter back to A-Z gets the lists sorted alphabetically again. So this here... is useless, plus superfluous it seems.