Those are two different release channels -- regular release and Extended Support Release -- so possibly each release of Firefox created/uses a different profile folder.

I suggest setting Windows to show hidden files and folders:

https://support.microsoft.com/en-us/help/14201/windows-show-hidden-files

Then paste this shortcut path to the Windows 10 system search box and press enter to load File Explorer in this folder:

%APPDATA%\Mozilla\Firefox\Profiles

Your Firefox 70 profile folder might be named with a random portion and then default or default-release. Double-click into that and then into the bookmarkbackups subfolder. The files here have the creation date coded into the name, along with the number of items (bookmarks + folders) in the file.

If you find one that you want to restore in place of your current set in Firefox 68 ESR, right-click > Copy it then right-click on your Desktop > Paste.

Then in Firefox 68, follow these steps to substitute the old set for your current set, using Restore > Choose File to fetch that backup from the desktop:

Restore bookmarks from backup or move them to another computer

Sorry I didn't ask the question specific enough. I am actually looking for an automatically way to restore from a bookmarks backup. My company has a lot users so I want to do it for them using command line or something similar.

Because you are replacing everyone's installation of Firefox?

Have you tested whether Firefox 68 ESR can successfully use the Firefox 70 profile folder instead of doing piecemeal migration? You may need to override downgrade protection. See:

• Dedicated profiles per Firefox installation
• Understanding in depth the profile per installation feature

I override the downgrade option and it worked. Thank you!

Note that it is never guaranteed that downgrading a profile works without problems even if you do not notice anything at first. This is done done a reason as some files or components may not be compatible anymore.