Detect and handle the case of our own typo correction extension being installed in parallel

lib/typoBootstrap.js

Index: lib/typoBootstrap.js
===================================================================
new file mode 100644
--- /dev/null
+++ b/lib/typoBootstrap.js
@@ -0,0 +1,89 @@
+/*
+ * This file is part of the Adblock Plus,
+ * Copyright (C) 2006-2012 Eyeo GmbH
+ *
+ * Adblock Plus is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * Adblock Plus is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/**
+ * @fileOverview Adds typo correction feature
+ */
+
+Cu.import("resource://gre/modules/AddonManager.jsm");
+
+let {Prefs} = require("prefs");
+let urlfixerID = "{0fa2149e-bb2c-4ac2-a8d3-479599819475}";
+let addonListener = null;
+
+function init()
+{
+  if (!Prefs.correctTyposAsked || (Prefs.correctTyposAsked && Prefs.correctTypos))
+  {
+    AddonManager.getAddonByID(urlfixerID, function(addon)
+    {
+      startTypoCorrection(addon && addon.isActive);
+    });
+  }
+  else
+  {
+    let onPrefChange = function(name)
+    {
+      if (name == "correctTypos" && Prefs[name])
+      {
+        init();
+        Prefs.removeListener(onPrefChange);
+      }
+    }
+    
+    Prefs.addListener(onPrefChange);
+  }
+}
+
+function startTypoCorrection(isInstalledAndEnabled)
+{
+  if (isInstalledAndEnabled)
+    require("typoFixer").detachWindowObserver();
+  else
+    require("typoFixer").attachWindowObserver();
+  
+  if (!addonListener)
+  {
+    addonListener = {
+      onEnabling: function(addon, needsRestart)
+      {
+        if (addon.id == urlfixerID)
+          startTypoCorrection(true);
+      },
+      onDisabled: function(addon)
+      {
+        if (addon.id == urlfixerID)
+          startTypoCorrection(false);
+      },
+      onInstalling: function(addon, needsRestart)
+      {
+        if (addon.id == urlfixerID)
+          startTypoCorrection(true);
+      },
+      onUninstalled: function(addon)
+      {
+        if (addon.id == urlfixerID)
+          startTypoCorrection(false);
+      }
+    }
+    
+    AddonManager.addAddonListener(addonListener);
+    onShutdown.add(function() AddonManager.removeAddonListener(addonListener));
+  }
+}
+
+init();