Here the answers:
Is there wireless involved?
Yes. 1 Computer connects with wireless, the other directly with an ethernet-cable.
And neither of them sees Firefly, or just the wireless one (since you just spoke about “the computer”, not about both)?
And what does the web interface say about Bonjours status?
(though I’m not sure if that is necessary or even correct, it’s showing “stopped” here currently and working anyway 😉 but probably should show “running”)