Radio boxes are turning into squares if I refresh the page on firefox

- Works fine if I go via a link https://matmoore.github.io/korean-study-cards/
- Broken if I go directly to the URL or refresh the page

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Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:61.0) Gecko/20100101 Firefox/61.0

Reproduce the issue by opening https://matmoore.github.io/korean-study-cards/ directly and by refreshing it in Firefox, then compare that with navigating there through a link. No source file or test is named; done means radio controls remain circular in both direct-load and refresh cases.

Written by the indexing model from the issue text.