gecko-dev/toolkit/components/thumbnails/test/browser_thumbnails_bug727765.js

/* Any copyright is dedicated to the Public Domain.
   http://creativecommons.org/publicdomain/zero/1.0/ */

const URL = "http://mochi.test:8888/browser/toolkit/components/thumbnails/" +
            "test/background_red_scroll.html";

// Test for black borders caused by scrollbars.
function runTests() {
  // Create a tab with a page with a red background and scrollbars.
  yield addTab(URL);
  yield captureAndCheckColor(255, 0, 0, "we have a red thumbnail");

  // Check the thumbnail color of the bottom right pixel.
  yield whenFileExists(URL);
  yield retrieveImageDataForURL(URL, function (aData) {
    let [r, g, b] = [].slice.call(aData, -4);
    is("" + [r,g,b], "255,0,0", "we have a red thumbnail");
    next();
  });
}