Comment 13 for bug 49613

If the drawable is an off screen XImage it will work. If the drawable is a
window the flicker will be unacceptable because there will be a long period
while the browser background is on screen. I'm told Windowless mode isn't
supported on Mac Classic for this same reason, flicker.

There are also needs to be a protocol on who ultimately puts the off screen
image on screen. I'm assuming it will be the plugin but I'm not sure what the
pro's and con's are.