gecko/browser/base/content/test/browser_bug419612.js

function test() {
  waitForExplicitFinish();

  Task.spawn(function () {
    let testPage = "http://example.org/browser/browser/base/content/test/dummy_page.html";
    let tab1 = gBrowser.addTab();
    yield FullZoomHelper.selectTabAndWaitForLocationChange(tab1);
    yield FullZoomHelper.load(tab1, testPage);

    let tab2 = gBrowser.addTab();
    yield FullZoomHelper.load(tab2, testPage);

    FullZoom.enlarge();
    let tab1Zoom = ZoomManager.getZoomForBrowser(tab1.linkedBrowser);

    yield FullZoomHelper.selectTabAndWaitForLocationChange(tab2);
    let tab2Zoom = ZoomManager.getZoomForBrowser(tab2.linkedBrowser);
    is(tab2Zoom, tab1Zoom, "Zoom should affect background tabs");

    gPrefService.setBoolPref("browser.zoom.updateBackgroundTabs", false);
    FullZoom.reset();
    gBrowser.selectedTab = tab1;
    tab1Zoom = ZoomManager.getZoomForBrowser(tab1.linkedBrowser);
    tab2Zoom = ZoomManager.getZoomForBrowser(tab2.linkedBrowser);
    isnot(tab1Zoom, tab2Zoom, "Zoom should not affect background tabs");

    if (gPrefService.prefHasUserValue("browser.zoom.updateBackgroundTabs"))
      gPrefService.clearUserPref("browser.zoom.updateBackgroundTabs");
    gBrowser.removeTab(tab1);
    gBrowser.removeTab(tab2);
  }).then(finish, FullZoomHelper.failAndContinue(finish));
}