gecko-dev/browser/base/content/test/general/browser_bug664672.js

function test() {
  waitForExplicitFinish();

  var tab = BrowserTestUtils.addTab(gBrowser);

  tab.addEventListener(
    "TabClose",
    function() {
      ok(
        tab.linkedBrowser,
        "linkedBrowser should still exist during the TabClose event"
      );

      executeSoon(function() {
        ok(
          !tab.linkedBrowser,
          "linkedBrowser should be gone after the TabClose event"
        );

        finish();
      });
    },
    { once: true }
  );

  gBrowser.removeTab(tab);
}