In my opinion there is a better way to solve this problem. I wrote more about the idea here but in brief we get rid of folder icons altogether and instead use shading for a folder visual cue. Bookmarks have no such shading while folders do. In the below example, the three left items are folders while the rest are bookmarks. By using emojis as folder names, in whole or in part, you can get as creative as you want and save a bunch of space.
