I can’t seem to make Thunderbird (supernova, flatpak) work with mailto links from my browser. The system handler correctly launches Thunderbird, but then, after a short wait time, a dialogue appears:

“Thunderbird is already running, but is not responding. To use Thunderbird, you must first close the existing Thunderbird process, restart your device, or use a different profile.”

If I do close down Thunderbird, then it works. But I’d expect to be able to have Thunderbird running.

Any ideas what’s wrong here?