I have two or three sets of bookmarks and would like to remove the duplicates.

I use the current version of Firefox on Ubuntu 22.04 Linux. When I scroll down past the individual bookmarks at the end of the menu, the folder names start repeating, along with the bookmarks inside them. I have three or four sets of bookmarks and would like to have only one. How can I delete all the bookmark folders below a certain point? By the way, when I install a new, different version of the operating system and sign in Sync restores all the bookmarks.