Hello!

If you wish to sort your bookmarks you will have to do it manually.

Click on CTRL+SHIFT+B then you will see all your bookmarks in this separe tab making it easier for you to sort them. Once your in this tab you can move them around, click on the DELETE button to delete any and you can also rightclick on the page and move down to the bottom and "sort" your bookmarks by name.

What you could do is to use sync to merge everything. Unless duplicates are in different folders, there should not be any duplicates.

https://support.mozilla.org/en-US/kb/how-do-i-set-sync-my-computer Sync your bookmarks, history, passwords, add-ons and open tabs with another copy of Firefox. Learn how to set up Sync.

https://support.mozilla.org/en-US/kb/how-do-i-choose-what-types-information-sync-firefox We'll show you how to choose which types of information (bookmarks, history, add-ons, and passwords) to share across all your devices through Firefox Sync.

https://support.mozilla.org/en-US/kb/firefox-sync-troubleshooting-and-tips

https://support.mozilla.org/en-US/kb/sync-firefox-bookmarks-and-browsing-history-iOS Sync your passwords, history, tabs and other browsing information across your iOS, Android and desktop computers with Firefox Accounts.