Secret URL Games don't work with Firefox

[louiidev]

Describe the bug
When trying to play a secret URL game in Firefox, it opens the game in a popup but shows a 404 page instead of the actual content

To Reproduce
Steps to reproduce the behavior:

1. Go to 'Open Firefox'
2. Go to a secret game 'https://{dev}.itch.io/{game}?secret={key}
3. Click the Run Game button
4. A Popup shows a 404 page error

Expected behavior
The game should open up in either the same window or in the popup as normal

Screenshots

Desktop (please complete the following information):

• OS: Windows
• Firefox
• latest, unsure what version