Unusual Thunderbird mail glitch (overenthusiastic scrolling) - any ideas

I have three panels on Thunderbird (v45.6.0). Full length on the left is the list of folders then on the right split horizontally are two - on the top it's the list of emails in the mailbox I'm viewing and the panel below is the email I'm clicked on.

Normally if I move the cursor into the email pane and start scrolling (even without clicking into the pane) the text of the email moves so that I can read the complete message. I've found that Thunderbird just scrolls up and down through the messages above, meaning that what I can see in the message pane changes. It's a bit frustrating.

It's been going on for a while but I noticed a few days ago that it seemed to have sorted itself out without me doing anything. Alas after switching off and on again I'm back to the overly excitable scrolly thing.

Additionally the rate of scroll is impressively fast, with the slightest touch on the mousepad (Lenovo, Windows 10) making the cursor leap to the top or bottom of the message, or mailboxes, list. This isn't a mousepad sensitivity problem because scrolling behaves normally in all other programs.

I'm hoping that if I don't switch off my computer for a few days it might settle down by itself but I don't know what's causing it or how to find the settings to interact with that aspect of it.

The only scroll options I've found make no difference, in any permutation.

 
Any ideas what's causing it, and what I might do to fix it? Thanks!