“Firefox is having trouble recovering your windows and tabs. This is usually caused by a recently opened web page.”
I’m seeing this more often now. FF 4.0.1 has a problem. It happens in any site with rich media, like Netflix. Some people are blaming this on plug-ins, Flash, and other things. I don’t know, FF 3.6 never had this problem with the same sites. Come to think of it, neither did 4.0.
Of course, it could be something else. I looked in Windows Event Viewer but did not see anything relevant.
Just did a Windows update, maybe something will shake out.
Google search for 4.0.1 crash