That should fix it:
https://github.com/discourse/discourse/pull/9529
Asking to a coworker to double check it fixes the issue, and I will then merge it and backport it into beta. It means this feature won’t be working for this user. We could probably make it work but given recent edge works I think this is OK, this fix ensures browser won’t crash if they don’t support any of the css selectors used in this feature.