http://kb.mozillazine.org/Unable_to_process_the_backup_file_-_Firefox

jscher2000 has a tool on his website to extract out your bookmarks and save them to an HTML-format bookmark export file. If you want to try it, here is the page:

https://www.jeffersonscher.com/res/bookbackreader.html

To open the bookmarkbackups folder in Finder, use the "Open in Finder" button in the first table on the Troubleshooting Information page, and double-click into bookmarkbackups where you should see several dated files. From there you can drag and drop onto the conversion tool.

To import the HTML file, see the steps in this article: Import Bookmarks from an HTML file.

I can save them to HTML and import. That is not the issue.. If imported, I end up with a complete double set of bookmarks. Or if from backup, it replaces everything with "old" data and erases some new bookmarks.

I would like to import certain bookmarks- not all.

Also, I'd like Firefox to stop deleting ransom bookmarks.

Are you using sync?

If you have sync, and there is a problem anywhere, Shut Down Sync Immediately On All Devices to prevent the problem from spreading. Once the problem is fixed, perform the same repair on all computers/profiles before using sync again.

[v57+] Places Maintenance is built into Firefox.

Type about:support<enter> in the address bar.

You will find Places Database near the bottom. Press the Verify Integrity button.

When done, copy and post the results here.

The old file, is it a normal jsonlz4 bookmarks backup, or is it an HTML file?

jsonlz4 file: http://kb.mozillazine.org/Unable_to_process_the_backup_file_-_Firefox

jscher2000 has a tool on his website to extract out your bookmarks and save them to an HTML-format bookmark export file. If you want to try it, here is the page:

https://www.jeffersonscher.com/res/bookbackreader.html

To open the bookmarkbackups folder in Finder, use the "Open in Finder" button in the first table on the Troubleshooting Information page, and double-click into bookmarkbackups where you should see several dated files. From there you can drag and drop onto the conversion tool.

To import the HTML file, see the steps in this article: Import Bookmarks from an HTML file.

HTML file: Whether you had an old HTML file, or just created a file using the above instructions:

Taz-D said

I would like to import certain bookmarks- not all.

Open the HTML file in a 'Word' type program. Go thru the file and Delete anything you don't want.

Now Save the file using a Different file name with an HTML extension.

Now when you import this new file, only what you want will be merged into the current Bookmarks. This will not replace anything already there.