diff -r 000000000000 -r 6474c204b198 toolkit/mozapps/extensions/test/xpinstall/browser_concurrent_installs.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/mozapps/extensions/test/xpinstall/browser_concurrent_installs.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,109 @@
+// Test that having two frames that request installs at the same time doesn't
+// cause callback ID conflicts (discussed in bug 926712)
+
+let {Promise} = Cu.import("resource://gre/modules/Promise.jsm");
+
+let gConcurrentTabs = [];
+let gQueuedForInstall = [];
+let gResults = [];
+
+let gAddonAndWindowListener = {
+  onOpenWindow: function(win) {
+    var window = win.QueryInterface(Ci.nsIInterfaceRequestor).getInterface(Ci.nsIDOMWindow);
+    info("Window opened");
+
+    waitForFocus(function() {
+      info("Focused!");
+      // Initially the accept button is disabled on a countdown timer
+      let button = window.document.documentElement.getButton("accept");
+      button.disabled = false;
+      if (gQueuedForInstall.length > 0) {
+        // Start downloading the next add-on while we accept this dialog:
+        installNext();
+      }
+      window.document.documentElement.acceptDialog();
+    }, window);
+  },
+  onCloseWindow: function(win) { },
+  onInstallEnded: function(install) {
+    install.cancel();
+  },
+  QueryInterface: XPCOMUtils.generateQI([Ci.nsIWindowMediatorListener])
+};
+
+function installNext() {
+  let tab = gQueuedForInstall.shift();
+  tab.linkedBrowser.contentDocument.getElementById("installnow").click();
+}
+
+function winForTab(t) {
+  return t.linkedBrowser.contentDocument.defaultView;
+}
+
+function test() {
+  waitForExplicitFinish();
+
+  Services.prefs.setBoolPref(PREF_LOGGING_ENABLED, true);
+  Services.wm.addListener(gAddonAndWindowListener);
+  AddonManager.addInstallListener(gAddonAndWindowListener);
+  registerCleanupFunction(function() {
+    Services.wm.removeListener(gAddonAndWindowListener);
+    AddonManager.removeInstallListener(gAddonAndWindowListener);
+    Services.prefs.clearUserPref(PREF_LOGGING_ENABLED);
+
+    Services.perms.remove("example.com", "install");
+    Services.perms.remove("example.org", "install");
+
+    while (gConcurrentTabs.length) {
+      gBrowser.removeTab(gConcurrentTabs.shift());
+    }
+  });
+
+  let pm = Services.perms;
+  pm.add(makeURI("http://example.com/"), "install", pm.ALLOW_ACTION);
+  pm.add(makeURI("http://example.org/"), "install", pm.ALLOW_ACTION);
+
+  gConcurrentTabs.push(gBrowser.addTab(TESTROOT + "concurrent_installs.html"));
+  gConcurrentTabs.push(gBrowser.addTab(TESTROOT2 + "concurrent_installs.html"));
+
+  let promises = gConcurrentTabs.map((t) => {
+    let deferred = Promise.defer();
+    t.linkedBrowser.addEventListener("load", () => {
+      let win = winForTab(t);
+      if (win.location.host.startsWith("example")) {
+        win.wrappedJSObject.installTriggerCallback = function(rv) {
+          gResults.push(rv);
+          if (gResults.length == 2) {
+            executeSoon(endThisTest);
+          }
+        };
+        deferred.resolve();
+      }
+    }, true);
+    return deferred.promise;
+  });
+
+  Promise.all(promises).then(() => {
+    gQueuedForInstall = [...gConcurrentTabs];
+    installNext();
+  });
+}
+
+function endThisTest() {
+  is(gResults.length, 2, "Should have two urls");
+  isnot(gResults[0].loc, gResults[1].loc, "Should not have results from the same page.");
+  isnot(gResults[0].xpi, gResults[1].xpi, "Should not have the same XPIs.");
+  for (let i = 0; i < 2; i++) {
+    let {loc, xpi} = gResults[i];
+    if (loc.contains("example.org")) {
+      ok(xpi.contains("example.org"), "Should get .org XPI for .org loc");
+    } else if (loc.contains("example.com")) {
+      ok(xpi.contains("example.com"), "Should get .com XPI for .com loc");
+    } else {
+      ok(false, "Should never get anything that isn't from example.org or example.com");
+    }
+  }
+
+  finish();
+}
+