Leechblock NG's redirect to Delaying page feature does not work

Steps to reproduce:

1. Install Leechblock NG.
   Chrome: https://chrome.google.com/webstore/detail/leechblock-ng/blaaajhemilngeeffpbfkdjjoefldkok
   Firefox: https://addons.mozilla.org/en-US/firefox/addon/leechblock-ng/
2. Open options and add any website (for example, YouTube.com) for blocking.
3. Set predefined URL to Delaying page in How to Block section. Also check if Block only first accessed page of site when delaying page is used option is selected (if it isn't, select it).
4. Select time for when to block. Save options.
   Expected behavior:
   On opening opening blocked website url, an HTML page with countdown for set time (default 60s) should run before webpage is opened.
   Orion, OS version; hardware type:
   Orion version: Version 0.99.110-beta (WebKit 613.1.12)
   OS version: macOS Monterey, version 12.1
   Hardware type: MacBook Air (13-inch, Early 2014)

Image/Video:

What opens in Firefox: