That extension may not be compatible with Nightly 55, as it hasn't yet been converted to WebExtensions format. My advice is to file an "Issue" with the developers of that extension here: https://github.com/fligtar/password-exporter/issues In a response to this "Issue" - https://github.com/fligtar/password-exporter/issues/75 - 18 days ago, one of the developers didn't even seen sure as to what a new WE API will support. IOW, the new API isn't complete just yet. That said, the Password Exporter extension can "export" into two file types; CSV and XML both of which are "human readable" in a simple text application such as Wordpad or Notepad. I have never used Password Exporter so I have no experience with the "output" of those "exports", but I have "read" both CSV and XML files in Wordpad to be able to "extract" data that I have needed. Overall, it would be a lot easier if you had a backup of your old Firefox Profile; you could just copy the '''logons.json''' file and the '''key3.db''' file into the new Profile ''(with Firefox closed, of course)''.