Firefox: What would be more secure/private: storing session cookies or saving password in the browser?

I am wondering, assuming the latest version of Firefox, which of the following options would be more preferable security-wise (e.g. assess and/or password to user account will be stolen) and which one privacy-wise (exposing user to the least advertisement tracking etc.): * Storing session cookies (i.e. logging in and never logging out), but not saving password & username in browser built-in Password Manager. * Saving password & username in built-in Password Manager (without Master Password) and setting cookies and site data to be cleared when browser is closed. P.S.: I am aware that using Master Password for password storage will increase security of the stored passwords. Though I am not wondering how to improve given options, but would like to asses them "as is".
http://dlvr.it/RzxCRb