So it turned out I was paying $40 per year to keep Norton functioning at the 2005 level?  Sweet.

Bought & installed Norton AntiVirus 2009,  and did Internet Settings > Intrusion Exclusions > unchecked all 3 boxes beginning with "HTTP Facebook."  Then went to Facebook and it is now functioning normally. 

It has done this before (as I said in my original post), i.e. returns apparently to normal for a short while, then freezes up again; so we'll have to see if this lasts.  In the meantime, thanks for all your help.

Bruce