On the positive side, this add-on respects separators and sorts within them. Auto-Sort Bookmarks does not respect separators. On the negative side, this add-on does not provide an option to exclude selected folders from sorting. Auto-Sort Bookmarks does provide that option.

Lacking an option to exclude folders, it's important to be able to manually sort the folders you want to exclude from automatic sort. However, this add-on will automatically resort your manually sorted folders every time you restart Firefox if you have the "Always keep sorted" option enabled. If you don't keep that option enabled, you'll have to manually sort each new bookmark.

Three stars for a good start, but this add-on needs more work (as does Auto-Sort Bookmarks).