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

...splaying a web page. r=

sfoster
It definitely fixes the issue. And you are correct, we do call getScreenshot() automatically but it's not completed when we call requestScreenshotURL. If you wait a little bit (by waiting for the data transfer icon to settle down, that usually indicates the page is loaded) and drag the card around, it will show the screenshot.

There are really two options here. I can add a method to browser_mixin that tells us when _screenshotBlob is set and calls us back or simply call getScreenshot() which already takes a callback.

Since this is *only* for 2.1 (works great in 2.2...) I am definitely leaning toward getScreenshot() and *not* adding new methods at this stage.