fune/docshell/test/browser/browser_bug134911.js

const TEXT = {
  /* The test text decoded correctly as Shift_JIS */
  rightText:
    "\u30E6\u30CB\u30B3\u30FC\u30C9\u306F\u3001\u3059\u3079\u3066\u306E\u6587\u5B57\u306B\u56FA\u6709\u306E\u756A\u53F7\u3092\u4ED8\u4E0E\u3057\u307E\u3059",

  enteredText1: "The quick brown fox jumps over the lazy dog",
  enteredText2:
    "\u03BE\u03B5\u03C3\u03BA\u03B5\u03C0\u03AC\u03B6\u03C9\u0020\u03C4\u1F74\u03BD\u0020\u03C8\u03C5\u03C7\u03BF\u03C6\u03B8\u03CC\u03C1\u03B1\u0020\u03B2\u03B4\u03B5\u03BB\u03C5\u03B3\u03BC\u03AF\u03B1",
};

function test() {
  waitForExplicitFinish();

  var rootDir = "http://mochi.test:8888/browser/docshell/test/browser/";
  gBrowser.selectedTab = BrowserTestUtils.addTab(
    gBrowser,
    rootDir + "test-form_sjis.html"
  );
  BrowserTestUtils.browserLoaded(gBrowser.selectedBrowser).then(afterOpen);
}

function afterOpen() {
  BrowserTestUtils.browserLoaded(gBrowser.selectedBrowser).then(
    afterChangeCharset
  );

  SpecialPowers.spawn(gBrowser.selectedBrowser, [TEXT], function(TEXT) {
    content.document.getElementById("testtextarea").value = TEXT.enteredText1;
    content.document.getElementById("testinput").value = TEXT.enteredText2;
  }).then(() => {
    /* Force the page encoding to Shift_JIS */
    BrowserForceEncodingDetection();
  });
}

function afterChangeCharset() {
  SpecialPowers.spawn(gBrowser.selectedBrowser, [TEXT], function(TEXT) {
    is(
      content.document.getElementById("testpar").innerHTML,
      TEXT.rightText,
      "encoding successfully changed"
    );
    is(
      content.document.getElementById("testtextarea").value,
      TEXT.enteredText1,
      "text preserved in <textarea>"
    );
    is(
      content.document.getElementById("testinput").value,
      TEXT.enteredText2,
      "text preserved in <input>"
    );
  }).then(() => {
    gBrowser.removeCurrentTab();
    finish();
  });
}