Expanding JSON payloads or inspecting them in the JSON tab seems to wreck JS falsy values (notably 0 and null) and display them as quoted empty strings ("").
For example, observe how the objectId and alert properties change as the tree is expanded:



Demonstrated in WebSocket Monitor 0.6.4 on FF dev edition 52.0a2.
Is all the TreeView behavior coming from the Firebug SDK? I don't know enough about extensions or React to trace the functionality very quickly here...