Bug 1078859 - Force getScreenshot for system browser window instances di...

...splaying a web page. r=

sfoster
I know the DOM of the card-view doesn't really "grow old" since we remove everything when exiting, but I'm always worried about leaving some inline styling laying around.
can you
* `screenshotView.style.opactity = ''` instead
* clear `style.transition` too (might have to wait for a `transitionend`)