2017-09-26 -- Enable Password Exporter 1.3.4 for Firefox 57 (Mostly Nonfunctional)
Another option for Firefox 57 is the Saved Logins dialog at about:preferences#privacy: • 2018-01-08 -- How to Look at the Stored Pa...
This has been tested with Firefox Developer Edition 57+.
Go to about:config and search for extensions.legacy.enabled
If it isn't present, create the setting as a boolean (right click anywhere free, New -- Boolean), and in any case set it to true to enable old extensions. Now exit/restart Firefox.
Go to the link to download Password Exporter, click "Download anyway", then open the XPI file (Ctrl+O) to add it to Firefox 57+:
https://addons.mozilla.org/en-US/thun...
You can also repeat the actions shown in the video to enable the extension yourself.