fune/browser/base/content/test/general/browser_bug533232.js

function test() {
  var tab1 = gBrowser.selectedTab;
  var tab2 = BrowserTestUtils.addTab(gBrowser);
  var childTab1;
  var childTab2;

  childTab1 = BrowserTestUtils.addTab(gBrowser, "about:blank", {
    relatedToCurrent: true,
  });
  gBrowser.selectedTab = childTab1;
  gBrowser.removeTab(gBrowser.selectedTab, { skipPermitUnload: true });
  is(
    idx(gBrowser.selectedTab),
    idx(tab1),
    "closing a tab next to its parent selects the parent"
  );

  childTab1 = BrowserTestUtils.addTab(gBrowser, "about:blank", {
    relatedToCurrent: true,
  });
  gBrowser.selectedTab = tab2;
  gBrowser.selectedTab = childTab1;
  gBrowser.removeTab(gBrowser.selectedTab, { skipPermitUnload: true });
  is(
    idx(gBrowser.selectedTab),
    idx(tab2),
    "closing a tab next to its parent doesn't select the parent if another tab had been selected ad interim"
  );

  gBrowser.selectedTab = tab1;
  childTab1 = BrowserTestUtils.addTab(gBrowser, "about:blank", {
    relatedToCurrent: true,
  });
  childTab2 = BrowserTestUtils.addTab(gBrowser, "about:blank", {
    relatedToCurrent: true,
  });
  gBrowser.selectedTab = childTab1;
  gBrowser.removeTab(gBrowser.selectedTab, { skipPermitUnload: true });
  is(
    idx(gBrowser.selectedTab),
    idx(childTab2),
    "closing a tab next to its parent selects the next tab with the same parent"
  );
  gBrowser.removeTab(gBrowser.selectedTab, { skipPermitUnload: true });
  is(
    idx(gBrowser.selectedTab),
    idx(tab2),
    "closing the last tab in a set of child tabs doesn't go back to the parent"
  );

  gBrowser.removeTab(tab2, { skipPermitUnload: true });
}

function idx(tab) {
  return Array.prototype.indexOf.call(gBrowser.tabs, tab);
}