FF 38.2.1 Passwords

I need an answer to this one:

On my computers I can go to my banking logon page, and I need to enter
the password, as expected (good). 

On my brother's computer, he goes to his banking logon pages (3 
different banks), and the password is alrady filled in, and it works 
(bad). I can find no trace of them in the Saved password list (I went 
back to 31.8.0, which works as expected), and I am pretty sure that 
there are no cookies with that information. Going back to 38.2.1 
brings them back. Where would that be saved? 

I cleared the cache. Deleting cookies for the site causes it to 
complain that cookies are not enabled (AFAICT they are).

I don't want to delete all of the passwords, if possible.

-- 
From the eComStation of Doug Bissett
dougb007 at telus dot net
(Please make the obvious changes, to e-mail me)