>A few seconds ago I saw there were 10 new messages. I clicked on the Messages button on the toolbar. I got the top pane treeview of the 10 messages in less than 1 second, but for the first message in the list of new ones to appear in the message pane at the bottom took about 15 seconds. That was longer than usual but I'd say the normal for me (using FF 45.0) to get that top message on a messages refresh has been averaging 5 - 10 seconds lately.

There is definitely something external.

The image shows the transactions you are making reference to. In the blue rectangle, the one when you pulled out those messages. All those are way under a second.