Log on/off the site

The past few mornings, I am frequently being asked to re-enter my username and password.  This isn't occurring the minute I start using the site.  Instead, I will log or blog something, it will update and then I will click on forums, friends, etc and it will log me off and ask for my information again.  A moment ago, I was surfing the forums and when I went to reply it sent me to the log in page. 

This has occurred 2-3 times each morning over the past few days.  I haven't changed my settings or anything on my computer.  Using Firefox on Mac OS X