'has-many' Relationship panel is empty on Firefox

I've noticed that the preview panel for a collection item's relationships doesn't render at all on Firefox, but seems fine on Chrome.

For this example, I have a simple Story -> Chapter * n -> Page * n content structure.

Before adding any relations is fine:

After adding some relations (Chapter -> Pages, in this example), nothing is displayed. Below is the result of adding two existing chapters, but not yet pressing 'Create':

The chapters do actually get added (confirmed by looking at the relations in the Chapter's mdoc entry) just nothing is rendered in the panel at all in the UI. Here's the result after hitting 'Create':

In Chrome, however, everything displays fine:

Start by reproducing the relationship preview issue in Firefox with the Story → Chapter → Page example, then compare the same panel in Chrome. Trace the collection item's relationship preview from the UI entry point and verify that existing relations render both before and after creation; done means the panel displays its relations consistently in Firefox and Chrome.