NS_ERROR_NOT_AVAILABLE exception when calling ctx.drawImage with a video

See https://observablehq.com/@severo/naive-face-tracking-and-extraction.

The call to context.drawImage(video, 0, 0, w, h); in the orig cell throws a NS_ERROR_NOT_AVAILABLE exception on Android Firefox 68.2.1, as described in https://stackoverflow.com/a/18580878/7351594.

I tried to apply the workaround (just waiting a bit - see the orig cell), but it doesn’t fix the problem, the exception keeps being thrown no matter how long I wait.

Could this problem be related with Observable? And even if it’s independent from Observable: did anybody see this case before?