Rated 4 out of 5 stars
If you are thinking about adding the ability to modify Bookmark folder icons, here is the method for doing that by manually editing your userchrome file. Maybe this will be helpful to you.
That would work. I've been working on another release that will fix most of the bugs thus far. Along the way, I've thought up at least two different (possible) methods of setting folder icons through an extension. This makes three! It is certainly possible