For form data, need security feature to not show the content (username/pw) until the first or 2 characters are typed? I don't like it when just clicking on username field shows it all and lets you log in!

I’ve saved Username and password for many sites in Firefox, and when I visit such
sites, I can just click on the username field and it automatically lets
me choose the username and password to log into the website. I thought that was not so
private especially if someone happen to be near my laptop when I’m not present (!).
Could anyone include a security/privacy option/feature wherein one has to type the
first or two initial characters in the username before Firefox lets you
see or click on the credentials? Of course having the current option to just click on username field to auto-fill is fine for those who are happy with it.
Thank you.