Developer reply by V@no
Rated 1 out of 5 stars
I think mozilla is stubborn, you should develop it for 57. or for opera and chrome - vivaldi
This review is for a previous version of the add-on (1.29.2). This user has a previous review of this add-on.The problem is 57 is exactly the same as Chrome and Opera, therefore not possible make something like MP+ with pathetic WebExtension APi
To create your own collections, you must have a Mozilla Add-ons account.