Firefox: making video fullscreen triggers the inview handler of the component underneath

[moloko]

for example, if you set your content up so that you have a full-width media component immediately followed by a block containing a component whose completion is based on inview then making the video fullscreen will trigger the inview handlers of the component(s) underneath.

interestingly the behaviour was slightly different depending on whether you make the video fullscreen using the button in the video player control bar or you right-click the video and select 'full screen' from the context menu. it was harder to trigger this bug using the context menu, it would really only work if the media component was scrolled partway out of the viewport like this:

[moloko]

Just to add to the fun here: if your text component is initially hidden by something like articleReveal then you get a slightly different problem in that inview will trigger for the text component, even though the text component isn't actually visible. And because the component's _isVisible property is set to false the call to setCompletionStatus will not actually do anything... which is fine, the real problem is that the inview handler still gets unregistered so it's then impossible to complete the component unless you either leave the page and come back to it or quit the course and relaunch.

This variation of the issue occurs in Chrome, IE11, Safari for iOS and Chrome for Android as well as Firefox

[moloko]

done in adaptlearning/adapt-contrib-media@de80875