I remixed the “Trello Card Snooze Power-Up” gitch, but when I try the Show Live button, I get a new tab and the blue loading screen for a moment then a blank page. The developer tools console log shows:
Failed to execute 'postMessage' on 'DOMWindow': The target origin provided ('https://trello.com') does not match the recipient window's origin ('https://scythe-gear.glitch.me').
Tried in Chrome 66 on Linux, MacOS and on Firefox on Linux. Same result on each.