Good news: 111.0b1 is the first beta with Supernova code. So there is a high chance the cause is Supernova code whose first daily build is 2023-01-16.
Bad news: I'm guessing the cause is straight up Supernova "ash" massive code landing on 2023-01-17. So you might try **nightly** builds on either side of 2023-01-17. If the problem is not seen there, use mozregression to try **nightly** builds between and 2023-02-27
(In reply to Frank from Matrix and #68)
> I narrowed it down to a change between Thunderbird 110_0b4 and 111_0b1.
That's good work.
Bad news: the number of [Firefox](https:/ /hg.mozilla. org/releases/ mozilla- beta/pushloghtm l?fromchange= FIREFOX_ 110_0b4_ RELEASE& tochange= FIREFOX_ 111_0b1_ RELEASE) and [Thunderbird](https:/ /hg.mozilla. org/releases/ comm-beta/ pushloghtml? fromchange= THUNDERBIRD_ 110_0b4_ RELEASE& tochange= THUNDERBIRD_ 111_0b1_ RELEASE) patches in that span is massive.
Good news: 111.0b1 is the first beta with Supernova code. So there is a high chance the cause is Supernova code whose first daily build is 2023-01-16.
Bad news: I'm guessing the cause is straight up Supernova "ash" massive code landing on 2023-01-17. So you might try **nightly** builds on either side of 2023-01-17. If the problem is not seen there, use mozregression to try **nightly** builds between and 2023-02-27
(above comment edited to remove duplicate text)