Milestone value doesn't appear in Firefox #2924

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Steps to reproduce in Firefox 74 with latest Refined GitHub (20.3.22):

1. Open an issue with a milestone set on a repo where you have edit access for milestones. For me it's https://github.com/jquery/jquery/issues/4453.
2. See that the milestone value doesn't show up. Only if you press the edit button you can see it on the list (see the screenshot).

The issue doesn't exist in Chrome 80 (with Refined GitHub 20.3.16) or in Firefox with the extension disabled.

<img width="256" alt="Screen Shot 2020-03-23 at 17 50 53" src="https://user-images.githubusercontent.com/1758366/77341441-026fe700-6d2f-11ea-846b-5f6b2b7afb6d.png"> <img width="329" alt="Screen Shot 2020-03-23 at 17 51 03" src="https://user-images.githubusercontent.com/1758366/77341445-03087d80-6d2f-11ea-8b7b-083d1245c8e4.png">