gecko-dev/docshell/test/browser/browser_bug852909.js

var rootDir = "http://mochi.test:8888/browser/docshell/test/browser/";

function test() {
  waitForExplicitFinish();

  gBrowser.selectedTab = BrowserTestUtils.addTab(
    gBrowser,
    rootDir + "file_bug852909.png"
  );
  BrowserTestUtils.browserLoaded(gBrowser.selectedBrowser).then(image);
}

function image(event) {
  ok(
    !gBrowser.selectedTab.mayEnableCharacterEncodingMenu,
    "Docshell should say the menu should be disabled for images."
  );

  gBrowser.removeCurrentTab();
  gBrowser.selectedTab = BrowserTestUtils.addTab(
    gBrowser,
    rootDir + "file_bug852909.pdf"
  );
  BrowserTestUtils.browserLoaded(gBrowser.selectedBrowser).then(pdf);
}

function pdf(event) {
  ok(
    !gBrowser.selectedTab.mayEnableCharacterEncodingMenu,
    "Docshell should say the menu should be disabled for PDF.js."
  );

  gBrowser.removeCurrentTab();
  finish();
}