Ok thanks for the info!
I've tried the first option, doesn't seem to be working for me.
I have a screencanvas with z-index 1, position:absolute(0,0) running a webgl context
and a regular canvas z-index 2, position:absolute(0,0) running a 2d context
the webgl context is visible, but not the regular 2d one. I've also tried using canvas instead of screencanvas, same result.
I will try option 2, as I think it's a better solution anyway.
It does work under webview+ (which i guess is to be expected).