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.
< Feedback on Youtube Playlists Sorted Alphabetically
Doesn't work on Vivaldi (Chrome)
Could you fix this? Works fine in Firefox, but not Vivaldi (Chrome).