Starting Thunderbird causes video problems

Stephen Hawkins

macrumors newbie
Original poster
Dec 31, 2019
I am running OS-X High Sierra on a iMac (21.5-inch, Mid 2011) 2.5 GHz Intel Core i5 with 12 GB of memory. If and only if I start Thunderbird 68.3.1 I get the blinking squares as seen in
These blinking squares frequently cover the entire screen and occasionally lock up the computer. If I never start Thunderbird I never have this problem.
It was suggested that I tell Thunderbird to use Hardware Acceleration. I found the option to "Use Hardware Acceleration when available". It did not help on or off. I still have the problem. This has been on going for a couple of months or more. During this time I updated OS-X any and all OS-X updates that came along and Thunderbird updates. I spent some time making sure it was not a hardware problem. I hate taking the iMac apart. It took me a while to prove to myself that it only happens when I start Thunderbird on my iMac with High Sierra. I have a Mac-mini (late 2009) with El Capitan and it does not have this problem. Both the iMac and the mac-mini have the same version of Thunderbird. It only happens on the iMac and it happens every time I start Thunderbird. The iMac was the one I used for email until I discovered it did not happen on the mac-mini.
Some times there are just a few blinking squares and sometimes it looks like the attached photos.