tor browser sandbox can't open downloads folder

I'm on Ubuntu 16.04 amd64 and clicking the folder icon in about:downloads does nothing, neither does clicking "Open Containing Folder".

the relevant lines in the console seem to be: firefox: Failed to open connection to session bus: /usr/bin/dbus-launch terminated abnormally without any error message firefox: * * (firefox:3): WARNING * *: Cannot launch default application: No application is registered as handling this file

Trac:
Username: femm

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