What the pocket "extension" (now integrated in FF) seems it would do, this actually does it. Pocket icon in the address bar gets red when something is bookmarked... looks cool, except that it is misguiding: when you open or refresh that same page again it is not longer red so you'll bookmark and tag it again. In My Pocket shows an icon next to the Pocket icon that actually gets blue when you visit that page again, letting you know that it was already bookmarked.
I uninstalled pocket for some years until I found this add-on could do this.
The other icon next to all extensions' icons display a list of pocketmarked list which is also convenient.
Thanks a lot for this Pierre-Adrien!