We currently show more events than we should be as backscroll. There are events leaking in from multiple sources, like decryption of older events.

We could also improve the backscroll loading by not displaying anything before a message that was sent by the current account.

Pushed by mkmelin@iki.fi:
https://hg.mozilla.org/comm-central/rev/42d76624220e
Improve Matrix catch up behavior. r=clokep

[Approval Request Comment]
Regression caused by (bug #):
User impact if declined: Matrix will show messages the user has already seen again and again and some messages may appear out of order.
Testing completed (on c-c, etc.): Minimal testing on c-c, patch not built on beta (but linted fine)
Risk to taking this patch (and alternatives if risky): Honestly, this is rather risky. because it's a big patch with changes deep in the matrix sync logic. I'm not quite sure if this should even be uplifted, since matrix is "preliminarily supported", but in the same vein, as long as it doesn't make it much worse, matrix is only preliminary.

Comment on attachment 9280652 [details] [diff] [review]
bug1770459-beta.diff

[Triage Comment]
Approved for beta

Thunderbird 102.0b5:
https://hg.mozilla.org/releases/comm-beta/rev/bb0f65091cfa