I get this message from this site (only this site) it usually pops right back after a moment, but sometimes it says: "website cannot be restored" and it X's out.
I know this doesn't help, but I have used Firefox, Chrome, Safari and Atomic for the past two years. I can't remember what a browser error even looks like.
I've noticed it does it a lot if I go mobile and then come back on pc. Not sure that makes a difference, but that is a correlation I have noticed and I run IE9.