You can arrange the bookmarks using Manage Bookmarks (or Ctrl-B) and move them around to your liking. It's a drag and drop kind of thing. Look for a line marker for where the dropped item will go.
That works for me.
Alex "People demand freedom of speech to make up for the freedom of thought which they avoid." -- Soren Aabye Kierkegaard (1813-1855)
Sounds like a need for that bookmark manager program that I was thinking about. Import all your bookmarks into it, categorize them, sort them how you want. Assign a browser to them if you wish. Then launch the browser from the bookmark browser program. It also could copy Bookmark URLs to the clipboard.
For: Columbine Bookmark Merge, \ufffd Gary Cramblitt
Have it; only briefly tried it, some time ago - it (then) purported to convert IE-->NS and vice versa; that was not my problem, however. But it seemed to work at organizing - it was only I who "didn't work" at achieving that :(
Files are dated 7/99.. so I have no idea how/if it would work with the likes of Mozilla now. Haven't bothered to see if an upgrade exists.
If I run into Drew's noted anomaly - maybe I'll look further. Right now - good intentions do not an 'organization' accomplish..