I have tried add-ons, but for me, the native workflow of selecting tabs with ctrl, right click to bookmark them to a folder and then close them all, and then later opening them from the bookmark manager is good enough. They added multi-select around Firefox 63 and it has improved this workflow to be pretty enjoyable.
* in the address bar (that is: 'star' 'space') will put you in bookmark search. I use tags prolifically and can search for keywords here and it works pretty well.
I guess I was not clear - what I do in the bookmarks manager is go into a folder, and select and open them in groups of 20 or so, then delete them as bookmarks. So bookmarks are sort of like "tab cold storage" for me. So for me tagging them would be wasted work since they will eventually be deleted regardless. I also do use bookmarks for the awesomebar but it is mainly so they are prioritized in normal autocomplete.
