Thunderbird beta does not open link

I have installed the Thunderbird beta (86.0b1) via the snap package on Ubuntu 20.04. I have used it for some months now without any issues. This morning, however, it suddenly opened with a brand new profile and even though my old one is still there I cannot open links from E-Mails anymore. Instead, it prompts me with an empty "Choose application" screen and if I browse to "/usr/bin/firefox" and select firefox, nothing happens. The same pop-up is shown when I try to change the http handler within the settings.