Open your Safari Prefs., select Autofil, select user names and passwords, and make sure that is checked. The first time that you go to a site, you will have to enter your login info manually so Safari can record it, after that, you should be good to go. I'm not a Safari user, so I don't know exactly how it works, but you might have to enter the first letter so that the browser knows what you are trying to do. Sometimes in Firefox, I have to enter the first letter of the "username" but FF always enters my Email address without any interaction. See if that will do what you want, if not you can follow the link above and set up some macros.