Similarly to what was discussed earlier this year, we have decided to update Thunderbird in all supported Ubuntu releases from 78.x to 91.x. This is a major version update.
Rationale
Thunderbird 78 is no longer supported by upstream, the last release in the series (78.14.0) having been released over 2 months ago. We don’t expect it to be practical to backport security fixes to LTSes indefinitely. It has therefore become necessary to move to Thunderbird 91.x.
Known downsides
This major new version does bring a number of improvements, UI changes and bug fixes, but we don’t expect any major disruption, unlike in the previous transition from 68.x to 78.x.
Users of Ubuntu 18.04, 20.04 or 21.04 not wishing to update beyond Thunderbird 78.x may instruct apt to hold or pin the package, but this is not recommended as the package will no longer receive security updates.
Background
This decision was discussed with the SRU team and it was agreed to use the normal security exception process, not the SRU process. It is tracked in bug #1949605 .
That’s right, this is a different topic, let’s not derail this thread. I don’t know whether the thunderbird deb will be dropped in favour in the snap in future releases, there’s no firm plan for this as far as I know, and in any case it would be discussed in a separate thread.
Just an FYI - at least one plugin will make Thunderbird 91 appear broken. I had to go through my plugins to find the culprit and it turned out to be one about hiding local folders - labeled as good for TB78+ but still broke TB.
So, if TB appears broken after the update, be sure to go through your plugins to see if one of those is the culprit.
I meant to mention this yesterday or the day before, but it slipped my mind where the thread was.