Check this link

• http://kb.mozillazine.org/Backing_up_and_restoring_bookmarks_-_Firefox#Restoring_bookmarks_from_backup

• https://support.mozilla.org/en-US/kb/restore-bookmarks-from-backup-or-move-them

Make sure that the backup file with the bookmarks has the correct file extension:

• .html for a HTML backup
• .json for a JSON backup

You can check the type via the right-click context menu of that file and open the Properties.
If you are not sure about the file type then you can open the file in Firefox via "File > Open File" A JSON backup will show as one long text line without line breaks and a HTML backup as a web page with clickable links.

A JSON backup starts with: {"title":"","id":1,"dateAdded":
An HTML backup starts with: <!DOCTYPE NETSCAPE-Bookmark-file-1>

Add quotes ("") around the name to rename the file to the correct file extension if the current file extension is hidden or if it is otherwise not working.
Verify the file type in the Properties via the right-click context menu to make sure that the change has been successful.

Thanks for the tip! I'll try this the next time I have access to the computer!

I opened the file in Firefox and according to the text content, it seems to be a JSON-file even though Firefox won't recognize it. I'll try to rename the file extension next time. Thanks!

I also was not able to restore my old bookmarks, which I tried to do so through the backups in the "Old Firefox Data" folder. I attempted to open the file bookmarks-2013-07-02.json but got the message that "To open this file, Windows needs to know what program to use. What do you want to do? 1) Use PC Health Advisor to find a program to open this kind of file or 2) Use Windows to manage this kind of file." When I click the first option, I get a list of software application options I can download in three categories, but I already have at least one in each category in my system. When I click the second option , I get sent to a Google search page that lists all kinds of websites about JSON files, none of which seems to provide a clear route to a solution.

I just tried adding quotes around the file name as per the above suggestion, but I got the message that a file name cannot include quotes. Also, for some reason, my file only contains the title and date added, none of the stuff in between that apparently is also supposed to be there.

In any case, shouldn't I be able to restore old bookmarks simply by clicking an older backup version under "Restore" under "Show All Bookmarks"? I also tried this, three times in fact, but got no results.