The older bookmarks.html file type still works for doing an Import of that file type. Firefox doesn't use that html format internally any longer, so users won't find a bookmarks.html file in their Profile folder unless a hidden preference is "toggled" on.

{ Ctrl + Shift + B } to open the Library window, then at the top use Import and Backup - click on Import Bookmarks from HTML ... and locate your HTML file. The Export to HTML... in Import and Backup still works for manually exporting bookmarks.

If you have a Bookmarks Backup file in .json or .jsonlz4 format, those file types need to be Restored; when doing that will overwrite any existing bookmarks that are on that Firefox installation.

Make sure the bookmarks backup file has the correct (lowercase) file extension:

• .html for a HTML backup (needs to be imported and merges bookmarks)
• .json for a JSON backup (needs to be restored and replaces bookmarks)

You can check the file 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 "Firefox > New Tab > Open File" or "File > Open File". A JSON backup will show as one long text line without line breaks and a HTML backup shows 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>

Verify the file type in the Properties via the right-click context menu to make sure the change has been successful. 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.