Brilliant idea, but name customization is necessary Rated 5 out of 5 stars
This idea allows to use bookmarking without opening dialog window and this is very strong advantage. But some customization is needed.
1. It is highly desired to give to user possibility to reassign the tagmarks names to his own names. I don't think it'll be big deal.
2. It is also desired that user can assign some other folder to this set of tagmarks, and not only Unsorted Bookmarks that is currently.
The reason why it is so necessary I can explain.
Usually user installs addons when he just have a lot of bookmarks with given names. In average he will just have about 1000 bookmarks and dozens tags when he finds your addon and decides to install it. He is highly interested to assert his most used tags and not to give birth to two dozens new. And reassign his old tags to new names he also doesn't want - he is accustomed, used to his own and it is difficult suddenly to change the names in mind and remember. That is why this is so important.
Now - regarding folder assignment (I mean one folder to all tagmarks).
The Unsorted Bookmarks folder isn't so easy accesible that in bookmarks toolbar and it is more convenient to use some other one.