There are in fact backups of the bookmarks. If you navigate to the following directory you'll see them.
C:\Users\USERNAME\AppData\Roaming\Mozilla\Firefox\Profiles\PROFILENAME\bookmarkbackups
Replace the words USERNAME with your computer's username and PROFILENAME will be the profile name of the Firefox install. If you just navigate to the C:\Users\USERNAME\AppData\Roaming\Mozilla\Firefox\Profiles directory it should be a no brainier at what your Firefox profile name is. There may be more than one. If you only have one FF profile then the folder containing the most crap is your profile. If you use more than one profile in FF, then you'll have to do some research based on extensions or what have you that are inside the profile folder. There may be an easier way to figure out what profile folder is which for each profile if you use more than one profile in FF, but I'd have to do some research on that.
Another way to get to your Firefox profile folder and the browser backups is to use the Everything.exe program and simply search for a file that exists in the FF profile. One such file will be key4.db. This file holds your passwords in encrypted form if you allow the browser to store your passwords. Even if you don't, that file should exist by default. And yes, it will carry some data weight to it whether you store passwords or not simply because it's a databases file and it has tables and what not. That's where the data weight comes in at. So in case you or someone else is wondering why it's some 200 KB and you save no passwords, that's why.
So fire up Everything.exe and search for the key4.db file. Now right click the file in Everything.exe and browse to its path. Presto, you're now in the FF profile area.
Keep in mind that if you have another Firefox browser derivative or Thunderbird installed there will in fact be more than one key4.db file. In which case the main folder you're looking for as it pertains to Firefox will be a folder named Mozilla.
Downloads - voidtools
If you want to use a bookmarks backup, simply copy and paste it to your desktop. Now in FF go to the top, Bookmarks | Show All Bookmarks | Import and Backup | Restore. Browse to the bookmarks backup file on the desktop.
By default, all of your backups should be listed there anyway. But in case you want to restore another bookmarks file, there ya go.