about the fullscreen feature

Hi the development team:
I have embed the example “vertex_colors” in my site in iframe, for some security reason, I am using the “sandbox” feature in iframe, and set sandbox=”allow-scripts” only, the example is in the same virtual host with my site , and I set “Header set Access-Control-Allow-Origin null” in litespeed static context field to avoid CORS , now the problem is in firefox, the fullscreen button couldn’t display and I found that “document.fullscreenEnabled” feature is false, but everything in chrome work fine, so how to set the fullscreen feature in firefox?

Any help would be appreciated!