Quelle  browser_download.js

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

var gTestRoot = getRootDirectory(gTestPath).replace(
  "chrome://mochitests/content/",
  "http://mochi.test:8888/"
);

function getFile(aFilename) {
  if (aFilename.startsWith("file:")) {
    var url = NetUtil.newURI(aFilename).QueryInterface(Ci.nsIFileURL);
    return url.file.clone();
  }

  var file = Cc["@mozilla.org/file/local;1"].createInstance(Ci.nsIFile);
  file.initWithPath(aFilename);
  return file;
}

function windowObserver(win, topic) {
  if (topic !== "domwindowopened") {
    return;
  }

  win.addEventListener(
    "load",
    function () {
      if (
        win.document.documentURI ===
        "chrome://mozapps/content/downloads/unknownContentType.xhtml"
      ) {
        executeSoon(function () {
          let dialog = win.document.getElementById("unknownContentType");
          let button = dialog.getButton("accept");
          button.disabled = false;
          dialog.acceptDialog();
        });
      }
    },
    { once: true }
  );
}

function test() {
  waitForExplicitFinish();

  Services.ww.registerNotification(windowObserver);

  SpecialPowers.pushPrefEnv(
    {
      set: [
        ["dom.serviceWorkers.enabled", true],
        ["dom.serviceWorkers.exemptFromPerDomainMax", true],
        ["dom.serviceWorkers.testing.enabled", true],
      ],
    },
    function () {
      var url = gTestRoot + "download/window.html";
      var tab = BrowserTestUtils.addTab(gBrowser);
      gBrowser.selectedTab = tab;

      Downloads.getList(Downloads.ALL).then(function (downloadList) {
        var downloadListener;

        function downloadVerifier(aDownload) {
          if (aDownload.succeeded) {
            var file = getFile(aDownload.target.path);
            ok(file.exists(), "download completed");
            is(file.fileSize, 33, "downloaded file has correct size");
            file.remove(false);
            downloadList.remove(aDownload).catch(console.error);
            downloadList.removeView(downloadListener);
            gBrowser.removeTab(tab);
            Services.ww.unregisterNotification(windowObserver);

            executeSoon(finish);
          }
        }

        downloadListener = {
          onDownloadAdded: downloadVerifier,
          onDownloadChanged: downloadVerifier,
        };

        downloadList.addView(downloadListener);

        BrowserTestUtils.startLoadingURIString(gBrowser, url);
      });
    }
  );
}