diff -r 000000000000 -r 6474c204b198 toolkit/mozapps/extensions/test/xpinstall/browser_offline.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/mozapps/extensions/test/xpinstall/browser_offline.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,61 @@
+let proxyPrefValue;
+
+// ----------------------------------------------------------------------------
+// Tests that going offline cancels an in progress download.
+function test() {
+  Harness.downloadProgressCallback = download_progress;
+  Harness.installsCompletedCallback = finish_test;
+  Harness.setup();
+
+  var pm = Services.perms;
+  pm.add(makeURI("http://example.com/"), "install", pm.ALLOW_ACTION);
+
+  var triggers = encodeURIComponent(JSON.stringify({
+    "Unsigned XPI": TESTROOT + "unsigned.xpi"
+  }));
+  gBrowser.selectedTab = gBrowser.addTab();
+  gBrowser.loadURI(TESTROOT + "installtrigger.html?" + triggers);
+}
+
+function download_progress(addon, value, maxValue) {
+  try {
+    // Tests always connect to localhost, and per bug 87717, localhost is now
+    // reachable in offline mode.  To avoid this, disable any proxy.
+    proxyPrefValue = Services.prefs.getIntPref("network.proxy.type");
+    Services.prefs.setIntPref("network.proxy.type", 0);
+    Services.io.manageOfflineStatus = false;
+    Services.io.offline = true;
+  } catch (ex) {
+  }
+}
+
+function finish_test(count) {
+  function wait_for_online() {
+    info("Checking if the browser is still offline...");
+
+    let tab = gBrowser.selectedTab;
+    tab.linkedBrowser.addEventListener("DOMContentLoaded", function errorLoad() {
+      tab.linkedBrowser.removeEventListener("DOMContentLoaded", errorLoad, true);
+      let url = tab.linkedBrowser.contentDocument.documentURI;
+      info("loaded: " + url);
+      if (/^about:neterror\?e=netOffline/.test(url)) {
+        wait_for_online();
+      } else {
+        gBrowser.removeCurrentTab();
+        Harness.finish();
+      }
+    }, true);
+    tab.linkedBrowser.loadURI("http://example.com/");
+  }
+
+  is(count, 0, "No add-ons should have been installed");
+  try {
+    Services.prefs.setIntPref("network.proxy.type", proxyPrefValue);
+    Services.io.offline = false;
+  } catch (ex) {
+  }
+
+  Services.perms.remove("example.com", "install");
+
+  wait_for_online();
+}