This add-on will not remember my user name in FireFox. (It does in Chrome. And it does in Edge.). I first reported this to Keeper three years ago when using it on a Win-7 laptop. I reported it again on a Win-8 desktop. I'm now have new hardware, running Win-10 on both laptop and desktop. It still won't remember the user name.
After three years and multiple notifications, it strikes me that Keeper has no commitment to solving the problem.
I'm forced to use browsers other than Firefox when I'm going to be doing a lot of log-ins; e.g. banking and ordering parts because it's quicker when the password manager remembers the user name.