Hi William, I assume those were not imported from Safari/Chrome, they are unique to your Firefox installation.

Is there anything in them? Do you have any add-ons that might have created those folders?

Has anyone else used your Firefox recently? Or, if you use Sync, do you share your account with anyone whose bookmarks might have merged with yours? You can check connected devices here: https://accounts.firefox.com/settings#connected-services

Hi,

What folders are you concerned about? Anyway, you can reorganize your bookmarks in the Library window at any time.