Description new function:
1. show sidebar
2. click on folder1
3. click on bookmarks in forder1
4. click od folder2 and autoclose folder1
5. click on bookmars in folder2
6. click od folder3 and autoclose folder2
7. click on bookmars in folder3

Description current state:
1. show sidebar
2. click on folder1
3. click on bookmarks in forder1
4. click od folder2 and stay opened folder1
5. click on bookmars in folder2
6. click od folder3 and stay opened folder2
7. click on bookmars in folder3

Or modify extension Bookmark Sidebar for Chrome to extension usable in Firefox. Author has not time to creation for Firefox
https://chrome.google.com/webstore/detail/bookmark-sidebar/jdbnofccmhefkmjbkkdkfiicjkgofkdh?hl=en
https://github.com/Kiuryy/Bookmark_Sidebar
Thank you Mipeli