Rated 4 out of 5 stars
One some pages, the stored login is not shown, after the page has been loaded. Only by choosing the context menu "Anmeldedaten ändern/change login data(?)" the login name shows up.
Also it would be nice if only the login name could be stored (without a password). An obvious work around is to store a wrong/short password.
1. This is covered both in the video linked from the description and in the FAQ (see support site).
2. Sorry, no can do. The password manager simply refuses to accept a login with a "null or empty" password. I can't change that. I guess the Mozilla developers figure there's no point in using a password manager and not putting passwords in it.