Sorry i gave you the wrong link. use this one. Remember log out first or the link will not work!
I just started having this problem today (firefox 3.6.10) but I've never had it here before ...I'm checking the "Remember Me" box every time.
I just did the big history and cookie dump needed to make firefox work with google instant. I'm wondering if the new cookie isn't being written on my machine correctly for one reason or another.