Rated 5 out of 5 stars
Excellent! I think, it's possible to add to it one simple thing: "Remove Favicon" should remove the favicon itself and not to leave empty rectangle.
By this way part of bookmarks/folders can be represented by favicons and part - by letters/words
"Remove Favicon" I mean remove favicon data. Firefox will automatic use the default favicon for it. For Firefox version 8 or more, default favicon is dotted square. For Firefox before version 8, default favicon is white paper. If you want real blank, just use "change favicon" and change to transparent gif or png. Note that it still take space 16 pixel. It will not collapse. I still don't know how to collapse individual favicon. I only know the way to collapse all favicon.