--- a/dom/apps/src/Webapps.jsm
+++ b/dom/apps/src/Webapps.jsm
@@ -9,16 +9,17 @@ const Cc = Components.classes;
 const Ci = Components.interfaces;
 const Cr = Components.results;
 
 let EXPORTED_SYMBOLS = ["DOMApplicationRegistry", "DOMApplicationManifest"];
 
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 Cu.import("resource://gre/modules/Services.jsm");
 Cu.import("resource://gre/modules/FileUtils.jsm");
+Cu.import("resource://gre/modules/WebappOSUtils.jsm");
 
 const WEBAPP_RUNTIME = Services.appinfo.ID == "webapprt@mozilla.org";
 
 XPCOMUtils.defineLazyGetter(this, "NetUtil", function() {
   Cu.import("resource://gre/modules/NetUtil.jsm");
   return NetUtil;
 });
 
@@ -166,17 +167,17 @@ let DOMApplicationRegistry = {
         break;
       case "Webapps:GetSelf":
         this.getSelf(msg);
         break;
       case "Webapps:Uninstall":
         this.uninstall(msg);
         break;
       case "Webapps:Launch":
-        Services.obs.notifyObservers(this, "webapps-launch", JSON.stringify(msg));
+        WebappOSUtils.launch(msg);
         break;
       case "Webapps:GetInstalled":
         this.getInstalled(msg);
         break;
       case "Webapps:GetNotInstalled":
         this.getNotInstalled(msg);
         break;
       case "Webapps:GetAll":

--- a/toolkit/Makefile.in
+++ b/toolkit/Makefile.in
@@ -19,16 +19,17 @@ PARALLEL_DIRS = \
   mozapps/extensions \
   mozapps/handling \
   mozapps/preferences \
   mozapps/plugins \
   mozapps/shared \
   obsolete \
   profile \
   themes \
+  webapps \
   $(NULL)
 
 DIRS += \
   mozapps/update \
   $(NULL)
 
 ifdef MOZ_MAINTENANCE_SERVICE
 DIRS += \

new file mode 100644
--- /dev/null
+++ b/toolkit/webapps/Makefile.in
@@ -0,0 +1,18 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+DEPTH     = ../..
+topsrcdir = @top_srcdir@
+srcdir    = @srcdir@
+VPATH     = @srcdir@
+
+include $(DEPTH)/config/autoconf.mk
+
+include $(topsrcdir)/config/config.mk
+
+EXTRA_PP_JS_MODULES = \
+	WebappOSUtils.jsm \
+	$(NULL)
+
+include $(topsrcdir)/config/rules.mk

new file mode 100644
--- /dev/null
+++ b/toolkit/webapps/WebappOSUtils.jsm
@@ -0,0 +1,81 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+const Cc = Components.classes;
+const Ci = Components.interfaces;
+const CC = Components.Constructor;
+
+let EXPORTED_SYMBOLS = ["WebappOSUtils"];
+
+let WebappOSUtils = {
+  launch: function(aData) {
+#ifdef XP_WIN
+    let appRegKey;
+    try {
+      let open = CC("@mozilla.org/windows-registry-key;1",
+                    "nsIWindowsRegKey", "open");
+      let initWithPath = CC("@mozilla.org/file/local;1",
+                            "nsILocalFile", "initWithPath");
+      let initProcess = CC("@mozilla.org/process/util;1",
+                           "nsIProcess", "init");
+
+      appRegKey = open(Ci.nsIWindowsRegKey.ROOT_KEY_CURRENT_USER,
+                       "SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Uninstall\\" +
+                       aData.origin, Ci.nsIWindowsRegKey.ACCESS_READ);
+
+      let launchTarget = initWithPath(appRegKey.readStringValue("InstallLocation"));
+      launchTarget.append(appRegKey.readStringValue("AppFilename") + ".exe");
+
+      let process = initProcess(launchTarget);
+      process.runwAsync([], 0);
+    } catch (e) {
+      return false;
+    } finally {
+      if (appRegKey) {
+        appRegKey.close();
+      }
+    }
+
+    return true;
+#elifdef XP_MACOSX
+    let mwaUtils = Cc["@mozilla.org/widget/mac-web-app-utils;1"]
+                    .createInstance(Ci.nsIMacWebAppUtils);
+    let appPath;
+    try {
+      appPath = mwaUtils.pathForAppWithIdentifier(aData.origin);
+    } catch (e) {}
+
+    if (appPath) {
+      mwaUtils.launchAppWithIdentifier(aData.origin);
+      return true;
+    }
+
+    return false;
+#elifdef XP_UNIX
+    let origin = Services.io.newURI(aData.origin, null, null);
+    let installDir = "." + origin.scheme + ";" + origin.host;
+    if (origin.port != -1)
+      installDir += ";" + origin.port;
+
+    let exeFile = Services.dirsvc.get("Home", Ci.nsIFile);
+    exeFile.append(installDir);
+    exeFile.append("webapprt-stub");
+
+    try {
+      if (exeFile.exists()) {
+        let process = Cc["@mozilla.org/process/util;1"]
+                        .createInstance(Ci.nsIProcess);
+        process.init(exeFile);
+        process.runAsync([], 0);
+        return true;
+      }
+    } catch (e) {}
+
+    return false;
+#else
+    Services.obs.notifyObservers(this, "webapps-launch", JSON.stringify(aData));
+    return true;
+#endif
+  }
+}

--- a/widget/cocoa/nsMacWebAppUtils.mm
+++ b/widget/cocoa/nsMacWebAppUtils.mm
@@ -32,8 +32,27 @@ NS_IMETHODIMP nsMacWebAppUtils::PathForA
     nsCocoaUtils::GetStringForNSString(temp, outPath);
   }
 
   [ap release];
   return NS_OK;
 
   NS_OBJC_END_TRY_ABORT_BLOCK_NSRESULT;
 }
+
+NS_IMETHODIMP nsMacWebAppUtils::LaunchAppWithIdentifier(const nsAString& bundleIdentifier) {
+  NS_OBJC_BEGIN_TRY_ABORT_BLOCK_NSRESULT;
+
+  NSAutoreleasePool* ap = [[NSAutoreleasePool alloc] init];
+
+  // Note this might return false, meaning the app wasnt launched for some reason. 
+  BOOL success = [[NSWorkspace sharedWorkspace] launchAppWithBundleIdentifier:
+                        [NSString stringWithCharacters:((nsString)bundleIdentifier).get() length:((nsString)bundleIdentifier).Length()]
+                        options: nil
+                        additionalEventParamDescriptor: nil
+                        launchIdentifier: NULL];
+
+
+  [ap release];
+  return NS_OK;
+
+  NS_OBJC_END_TRY_ABORT_BLOCK_NSRESULT;
+}

--- a/widget/nsIMacWebAppUtils.idl
+++ b/widget/nsIMacWebAppUtils.idl
@@ -12,9 +12,14 @@ interface nsIMacWebAppUtils;
 
 [scriptable, uuid(e9096367-ddd9-45e4-b762-49c0c18b7119)]
 interface nsIMacWebAppUtils : nsISupports {
   /**
    * Find the path for an app with the given signature.
    */
   AString pathForAppWithIdentifier(in AString bundleIdentifier);
 
+  /**
+   * Launch the app with the given identifier, if it exists.
+   */
+  void launchAppWithIdentifier(in AString bundleIdentifier);
+
 };