Firefox 71.0 and saved logins

[Dave Tyson <dtyson%anduin.org.uk@localhost>]

I seem to have found a particularly irritating issue with firefox 71.0 on 
amd64 under NetBSD-current NetBSD-8 (and probably 9 - but not tested)

If you go to a website which needs a password FF will dutifully ask if you 
want to save it. If you do then it will fill in the username/password field on 
subsequent occasions correctly. 

If you go to preferences -> logins and passwords and ask to see a list of
saved logins it reports there are none. You cannot add new entries either.

There a message on the console (if you start from a shell):
Javascript error: resources:///modules/AboutLoginsParent.jsm, line 185 Error: 
AboutLoginsParent: Subscribe message the remote type didn't match 
expectations: null == privelegedabout

which might be significant.

Not sure how to fix this but its a real PITA. Anyone else seeing this?

Dave