Folders = topics, of course.
I put whatever I want a bookmark for in a topic. Call it folder if you want. Subject heading is best term, IMHO.
There is bookmarks toolbar and bookmarks menu. Bookmarks menu is one place that has the subdivisions, aka topics, folders, subject headings, or whatever term works.
As I said I have topic headings for each Atlantic Canadian province. & I have one for Camping and the example I gave I want each province's webpage for regulated fuel prices in both the appropriate provincial topic heading and in the camping topic heading.
This stupid version of Firefox thinks that you only need to put a bookmark under one topic heading. Who the heck thinks the same way every day? It will only let you put one webpage be bookmarked under one topic. If you try to save a bookmark for one page under more than one topic it deletes what's already there. That's what is wrong.
:(