OS: Linux Debian
ThunderbirdVersion: 78.14.0 (64bit)
Problem at start-up of thunderbird: "messengerID=windowsID"
Problem occured since: After changing display environment variables (to set up display X-server for LXC-container)
Solution: Deletion of "addonStartup.json.lz4" in .thunderbird/<profile-folder>/addonStartup.json.lz4
addonStartup.json.lz4 is automatically replaced in folder after restart. Everything works.