Thank you, StaticGuy. There are at least 3 other threads on the forum which contain the same message: Vista 32, latest SP, computer freezes while browsing with Chrome, Firefox, or Opera.
I have had to force hard boot numerous times. Rolled back to 2218 and ALL the problems vanished. It seems that 2233 and its predecessor are incompatible with Vista 32. This is confirmed by other users on these threads.
Never used anything except Avast free on this laptop. Never had infections (I check with Malwarebyte free as well.)
Avast should pay attention to these bugs. It hadn't fixed them in the last 2 versions - hope it does in the next one.
Many thank yous.
Yarok