Something has changed in your browser settings, making it delete or not save cookies.  I have mine set up to clear cookies every time the browser is closed, and I have always had to log in every time. 

Did your brower update while you were down?  When Firefox updated across versions on me, lots of stuff got foreign to me for a little while.  There's some stuff I really wish I could put back like it was, but I have not figured out how.