Hi @pkimmel,
Starting off let me confirm my understanding. You are asking about 2 items:
First, that the renderer is not working in Firefox.
And second, that you are not able to capture the error and handle it accordingly.
Is this correct?
To answer the first question about the renderer not working in FF, there is some useful trouble shooting instructions in this thread "Browser supports WebGL, but initialization failed" in Chrome but not FF/Edge - #5 by James_B
On the second question regarding capturing and handling the error, we have a setting which if off by default which when enabled does the following
Exceptions occurring in render are always caught in order to raise the renderError event. If this property is true, the error is rethrown after the event is raised. If this property is false, the render function returns normally after raising the event.
https://cesium.com/learn/ion-sdk/ref-doc/Scene.html?classFilter=scene#rethrowRenderErrors