Update, Thursday, 18 March 10 pm
A crash the afternoon of 15 Mar. when reading a message in Thunderbird.
A crash upon the first use of Firefox after hibernation, the evening of 16 Mar.
Later in the enening of Mar 16, I removed AVG9 and installed Avast! free.
I have used Firefox extensively since then with no problems. I started using Thunderbird the evening of 18 Mar with no problems so far.
I'll wait a few days before installing the inkjet printer driver.
seacue