In Firefox 23.0.1, sometimes it will autofill my yahoo username and password, sometimes it won't

The website may be using autocomplete=off to prevent Firefox from saving and automatically filling the name and password.<br /> If you have previously saved a name and password then you should at least get a drop-down list if you click in that form field (you may first have to click elsewhere to remove the focus from this input field). You can remove autocomplete=off with a bookmarklet to make Firefox save names and passwords and other form data. *http://kb.mozillazine.org/User_name_and_password_not_remembered Also make sure that you do not run Firefox in (permanent) Private Browsing mode (Never Remember History). *https://support.mozilla.org/kb/Private+Browsing