For some reason, whenever you go to https://publisher.yahoo.com/ it won't remember your password or auto fill, like AdSense. They programmed not to allow it for some reason. A thread at WebmasterWorld named Is there a direct link to the login? gives an other option.
I am not sure how secure it is to have this on your computer, you make that call.
<form method=post action="https://publisher.yahoo.com/portal/login.php" name=verify_form>
<input type=hidden name=username value=your_username>
<input type=hidden name=password value=your_passwd>
You can just save it locally or put it onto a https server
Forum discussion at WebmasterWorld.