This is frustrating. I can't find the way....
Try this: In your FF profile, open the file
bookmarks.html in Open Office Calc. Filter (Data>Filter) to include only non empty rows.
If you have folders within your Bookmarks directory, you'll have to delete them from the spreadsheet manually because the sub-folder occupies a row in Calc.
I have 3122 Bookmarks
These go back many years and many are kaput!
EDIT: You can probably do the same routine in Excel.
EDIT2: I did not try to open all 3122 Bookmarks; my cheapa## Qwest modem just now cooled down to 100 deg F, or so
