Firefox has two parallel options:

Export and Import

This uses an HTML file format dating back to the previous millennium, and import adds the bookmarks in the file, possibly to an "Imported Bookmarks" folder at the end of the Bookmarks Menu, to what is already in the browser. See:

• Export Firefox bookmarks to an HTML file to back up or transfer bookmarks
• Import Bookmarks from an HTML file

I think this is probably what you did the last time.

Backup and Restore

This uses a proprietary format that only Firefox understands, and restore does a complete wipe and replace. See: Restore bookmarks from backup or move them to another computer.

Would that work better for you? If you don't intend to use the bookmarks in other browsers, maybe it would.

But if you need to add them non-destructively to an existing installation, then not directly. I created an unofficial converter in case you need an export-format HTML file and only have a .json (or .jsonlz4) backup file. See: https://www.jeffersonscher.com/ffu/bookbackreader.html

jscher2000 - You're right about the HTML import, that's what happened. Unfortunately none of this really helps me, but it's good to have an established knowledge base on the topic, so thank you for a speedy response! I appreciate it.

Hopefully Firefox gets an upgrade soon, because this is a bit ridiculous, browser stuck in 2000s with some of the basic features, it's not good

What do you see if you open the file in a Firefox tab?

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

Unfortunately none of this really helps me

Well, what is the remaining problem?