[CentOS] My linux keeps logging me off when I run Firefox (how to debug)?

This is a strange one to me.

Just recently, my Centos 6 has been "gentle crashing" where it doesn't crash, 
per se, but the screen goes black, and the login prompt pops up. 

It only happens when I run Firefox and it only started happening this morning.
However, it has happened a dozen times, and always when Firefox is running.

It does NOT happen when Firefox is not running. 
I haven't tested with Chrome yet; so that's my next test - but - the 
question I have is:

How do I log the events that are causing Centos to log me out of 
user1 and to present the login screen?