How did you create the backups -- using Backup (to a .json file) or Export (to a .html file) or both?

By any chance, did you copy anything from your old profile folder, especially the bookmarkbackups folder?

Make sure that the backup file with the bookmarks has the correct file extension: .html for a HTML backup and .json for a JSON backup.
You can check that 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. You can verify the file type in the Properties via the right-click context menu.

To try and answer both replies. I used Firefox Open File in the (File) drop down menu and opened the file that I saved with a JSON file extension and this is a sample of what I got.

{

   "title": "",
   "id": 1,
   "dateAdded": 1269983062828000,
   "lastModified": 1321058301468000,
   "type": "text/x-moz-place-container",
   "root": "placesRoot",
   "children": [
       {
           "title": "Bookmarks Menu",
           "id": 2,
           "parent": 1,
           "dateAdded": 1269983062828000,
           "lastModified": 1335826329859000,
           "type": "text/x-moz-place-container",
           "root": "bookmarksMenuFolder",
           "children": [
               {
                   "title": "Recently Bookmarked",
                   "id": 16768,
                   "parent": 2,
                   "annos": [
                       {
                           "name": "Places/SmartBookmark",
                           "flags": 0,
                           "expires": 4,
                           "mimeType": null,
                           "type": 3,
                           "value": "RecentlyBookmarked"
                       }

This looks like what cor-el posted as what a JSON file looks like. How come Firefox won't open it as a restore when it will open it under the File menu? I just tried right clicking on the 3 versions of the file on my desktop. The one above that I opened in Firefox shows in the Properties Box as a JSON File. I tried to restore it and it still comes up with the same error message. It has a place to name the program to open it. I tried Firefox as the program and it still would not restore the file. What program should I be using? Where can I find it? Thanks for the replies.

Also to answer jscher2000 question. When I saved the file originally I let the program put the JSON extension on the file. I did not save it in HTML format. I just saved three versions of the file under 3 different file names. Later when I could not restore the file I manually added the JSON extension to one of the saved files. I am not quiet sure why the file extension does not show up in the Properties box for all the 3 copies I made. The only one that shows up with a JSON extension is the one I did manually. When I open the Properties box on the two without the JSON extension, where it says File Type out to the side where the extension name should be it just says File

As far as copying the Old Profile Folder and Bookmarks Backup I did not do this. Is there a chance that this Folder still exists or was it copied over when I reinstalled Firefox? Thinking that Firefox might have automatically renamed the file to preserve it.

Did you verify in the Properties that the file type of that file is a JSON file type?

Windows has a habit to hide some file extensions and renaming such a file won't change the file type.

• http://kb.mozillazine.org/Show_hidden_files_and_folders

I went through the process you outlined. On My Computer/User/Desktop there is a file Name= bookmarks-2012-04-28; Size=137kb; Type=JSON I also did the right click properties on that file and it shows up as Type=JSON File.

I did a search of my C: Drive looking for any *.JSON files and the search did not find this file which makes me think that it is not really a JSON file extension. If you don't mind please walk me through renaming a file with the extension. I thought I knew how to do this, but maybe not since I can't seem to call this file up. Just a point of information. The other two saved files that I did with the backup function for bookmarks do not show up as JSON files only as a file when I go through My Computer to look for the files. I also followed up on jscher2000's idea of checking the profile section of Firefox. There was not an old version of my bookmarks file stored in the profiles that I could find. So that is a dead end also.

If you set Windows (temporarily) to show all file extensions ("Hide extensions for known file types") then you should be able to rename the file properly. You can also add quotes around the name ("bookmarks.json") to force a file extension.

• http://kb.mozillazine.org/Show_hidden_files_and_folders

I have tried renaming the file with the .JSON extension. The My Computer file list shows the file with the JSON extension. When I go back to Firefox in the Bookmarks and try to restore the file it still gives me the "File Not Supported" error message". Is there a way to open the file in some other program and then save it as an HTML document and then import it back to FireFox? Can I just copy the file I have with the JSON extension and copy it to the Firefox Profile Folder and delete the file that Firefox created in the Profiles Folder?

Ok I went through opening the profiles and copying one of the .JSON backups to the folder where FireFox stores that info. The file appeared to copy without any problems. I closed all the windows and shut Firefox down. I restarted Firefox and the file did not show up in the list of files to restore. So that idea did not work. I am running out of possibilities.

SOLVED THE PROBLEM. When I was renaming the files I used capital letters because that was what showed up in the drop down box when I originally saved the backups. I went back to the profiles file and realized the other backups were all in lower case (.json) so I renamed the file I had moved from the desktop and used the lower case letters, went back to Firefox and the file showed up and restored perfectly. Sorry to have been so much trouble. Thanks for everyones help

Can I just copy the file I have with the JSON extension and copy it to the Firefox Profile Folder and delete the file that Firefox created in the Profiles Folder?

Firefox stores your bookmarks in a database named places.sqlite, so copying your .json file into your profile folder won't actually import them into your bookmarks list.

I don't understand how a file you created using the Backup feature of the Bookmarks Manager cannot be reimported using the Restore feature of the Bookmarks Manager. Unless the file got corrupted somehow.

One thing that seems strange is how widely spaced your .json data is. Usually it is packed into a single long line. Did you open and save the file in another program that could have changed the format? As a test, I hand-edited one of my .json backup files by adding line breaks and spaces and was still able to restore it, so the restorer can deal with some changes to the file, but maybe something more critical was lost (such as closing brackets or braces). Hmmm...

Edit: Glad to hear you solved it.

Firefox will use the most recent JSON backup in the bookmarkbackups folder to create a new bookmarks database if you delete or (re)move all places files in the Firefox Profile Folder.