Following on from #1226

Unfortunately, I'm at a total loss on my end. Here are my tests so far:

• macOS 12.6 (colleague's laptop):
  • Firefox: works
• macOS 15.2 (my laptop):
  • Chrome: doesn't work
  • Firefox: doesn't work
  • Firefox DE: doesn't work
  • Safari: doesn't work
• macOS 15.3 (colleague's laptop):
  • Firefox: works
• Windows 11 (PC1):
  • Chrome: works
  • Firefox: works
• Windows 11 (PC2):
  • Chrome: doesn't work
  • Firefox: doesn't work

I can't see any common links between any of the test cases. No console errors, no assets being blocked or failing to download. The issue is that the .show CSS class isn't being added to the modal, or the modal backdrop.