In which way could Mozilla be coerced in building a backdoor into its software by the Australian government, in a way not being seen by the public? I can't imagine that an Australian law would either lead to shutting down open source projects nor lead to make them (or parts of it) closed source. Would Signal do this? I don't think so, they'd loose all trust immediately.

The only problem I see is that open source projects might not accept contributions from Australian residents or citizens.