I have found the real reason and fix for this issue!
It seems that it is caused by no permissions for ~/.cache/ibus/dbus-* socket. But for some weird reason, the issue happens only if abstractions/dbus-session is included in the torbrowser.Browser.firefox AppArmor profile file.
Adding this line into torbrowser.Browser.firefox seems to fix the issue without any side effects:
owner @{HOME}/.cache/ibus/dbus-* rw,
(This line is also present in the official Firefox AppArmor profile, but missing from the torbrowser-launcher one.)
I have found the real reason and fix for this issue!
It seems that it is caused by no permissions for ~/.cache/ ibus/dbus- * socket. But for some weird reason, the issue happens only if abstractions/ dbus-session is included in the torbrowser. Browser. firefox AppArmor profile file.
Adding this line into torbrowser. Browser. firefox seems to fix the issue without any side effects:
owner @{HOME} /.cache/ ibus/dbus- * rw,
(This line is also present in the official Firefox AppArmor profile, but missing from the torbrowser-launcher one.)