Thunderbird 60 slow scrolling and opening messages, high CPU, generally slow after upgrade to Fedora 28 (linux)

After upgrading my Fedora to 28, and my Thunderbird to the latestest in the repos (60.3.1), I get very poor performance scrolling through the interface and opening mails. The entire interface is sluggish. Rebooting in safe mode makes no difference. With TOP running, I can peg one CPU core just by scrolling or navigating between folders.