Progressively slowing down, massive memory leaks, message pane blacking out

Hi Everyone, just recently happened after the last update to 52.1.1 - has been fine for years prior. The more messages I scroll through / read, the slower Thunderbird becomes, to the point where the message pane simply remains black and does not show the next message. At that point I need to either quit or force close Thunderbird, Memory usage goes up - 183 MB at load time, around 700 MB after viewing 20-25 messages then crashes a little beyond that. Suspect it's the memory leaks driving the black message panes and slowness. Happens during safe mode as well - so not the add-ons. Any insights would be appreciated!