I rarely use IE9 but IIRC there is a setting in auto complete about user names and passwords.

I use Firefox 9 and with some sites I must click on a field twice to get it to auto fill while on others I don't. I have no idea what causes this. Perhaps there is something in the web page script that causes such behavior.

Auto complete is handy, but don't use it for logon information. Allowing user ID's and passwords to be stored in a browser is like having no security at all.