okay, try this... if you want the fastest way and dont wanna see the process, just skip to right after the last step to see the shortcut lol
1. go to windows explorer (computer)
2. C drive
3. press alt to open the file/edit/view/etc bar.
4. go into tools, folder options
5. go to the view tab
6. in the hidden files and folders section, make sure you can see hidden files
7. press ok, exit out, etc.
8. C:\Users
9. Find your username, in my case it is Brian, so i go to C:\Users\Brian
10. There is a folder that was hidden called AppData, go there
11. Now go to the Roaming folder
12. In there find the Mozilla folder
now its C:\Users\Brian\AppData\Roaming\Mozilla
13. Firefox folder
14. Profiles folder
15. pak8s4ok.default folder
now its C:\Users\Brian\AppData\Roaming\Mozilla\Firefox\Profiles\pak8s4ok.default
16. should be a Bookmarkbackups folder, and there should be a few files there, all are backups of your bookmarks.

id think the last one in the list is the most recent. They are JSON files
so in the end you are in
C:\Users\Brian\AppData\Roaming\Mozilla\Firefox\Profiles\pak8s4ok.default\bookmarkbackups
if you want you can just replace 'brian' there with your username that appears in the C:\Users folder, and you'll go right to it

hope that works!