Thunderbird released version 140.7.2 yesterday to follow Firefox 140.7.1 which fixes a security issue, a heap buffer overflow in libvpx. That's a video codec. The Thunderbird folks wrote this in their advisory:
In general, these flaws cannot be exploited through email in the Thunderbird product because scripting is disabled when reading mail, but are potentially risks in browser or browser-like contexts.
So, only Betterbird users who use Betterbird as a web browser, or browsing news feeds with embedded videos may be affected. Since the security risk is extremely low and since Betterbird 140.8.0esr-bb19 will ship before the 24th of February 2026, we decided to skip this release.
The "colourful" picture shows the all the test failures that occurred in Thunderbird's release automation and are shown in the so-called "treeherder" (dashboard). Each orange box is a test failure, and it's not advisable to ship the product with so many test failures without investigating them.
In other words: Even if we had built Betterbird based on this Thunberbird release, it could be quite broken. BTW, this is not the first release chagrin, refer to these earlier articles [1] and [2] for more.
Update: Apologies to the Thunderbird folks for the incorrect statement above. We heard that the test failures were analysed and that they came to the conclusion that despite what was displayed on the dashboard, the product showed no functional failures and was safe to ship. That was confirmed by their QA team, in fact, we also tested that Thunderbird release and didn't see failures.
Our article was overreacting to the fact that in the past, test failures were ignored and the product did get shipped with minor functional issues.