How to make this setting stick

Every time I come into the forums, I have to log in. Is there a way for the system to remember us? Also, how do we make our preferences in the dropdown stick?

Every time I come back in it's set for "Relevance" which to me means nothing. Relevant to what? So, I can set it to "Latest" but as soon as I go into a thread and hit the back button to come back to the thread list, it's defaulted back to "Relevance".