I run multi-boot Debian fairly standard installations, one Stretch and one Buster. The Stretch installation is rock solid and I keep it until I'm 100% confident that Buster is stable enough to rely on for production use. Although Stretch is XFCE and Buster is KDE, they're otherwise pretty similar, with essentially the same software packages, or equivalents, so that I can do my work in either one.
I use Thunderbird for email and my profile with all the emails resides on a data disk which I've been able to link to with any installation of Thunderbird. Until now.
In version 68, Mozilla changed the ability to do what I've been doing, making access with an earlier version impossible, once the profile has been accessed by an installation of version 68 (or later), and locking that profile to a specific installation. So accessing the profile and emails from multiple installs is no longer an option. What's worse is that it just happened that I updated the Stretch installation before the Buster one so my profile is now locked to Stretch and I can't get to it from Buster.
Curiously, both versions of Thinderbird are the same at 68.2.2 but it looks like Mozilla interpret 68.2.2-1~deb9u1 as later than 68.2.2-1~deb10u1.
I can, of course, access my email via the Stretch installation, so it's not like I've lost it, but it is a huge inconvenience and, looking forward, is making me think that I need to change to a different email client. In the short term, initial investigation seems to indicate that I can import, folder by folder, if I create a new profile. With circa 9000 emails and multiple identities and folders this is going to be quite a task.
So, has anyone else been caught out the same way? And have you come up with a strategy to recover and retain similar functionality in the future?
I'm sure Mozilla have some good reason, but considering users doesn't seem to enter their minds. What were they thinking?