diff --git a/b2g/chrome/content/desktop.js b/b2g/chrome/content/desktop.js
index 662569826435..3e0d0234e546 100644
--- a/b2g/chrome/content/desktop.js
+++ b/b2g/chrome/content/desktop.js
@@ -52,6 +52,10 @@ function checkDebuggerPort() {
   // DebuggerServer.openListener detects that it isn't a file path (string),
   // and starts listening on the tcp port given here as command line argument.
 
+  if (!window.arguments) {
+    return;
+  }
+
   // Get the command line arguments that were passed to the b2g client
   let args = window.arguments[0].QueryInterface(Ci.nsICommandLine);
 
diff --git a/b2g/chrome/content/runapp.js b/b2g/chrome/content/runapp.js
index 59340763db51..6df206fb1cb6 100644
--- a/b2g/chrome/content/runapp.js
+++ b/b2g/chrome/content/runapp.js
@@ -5,6 +5,10 @@
 
 let runAppObj;
 window.addEventListener('load', function() {
+  if (!window.arguments) {
+    return;
+  }
+
   // Get the command line arguments that were passed to the b2g client
   let args = window.arguments[0].QueryInterface(Ci.nsICommandLine);
   let appname;
diff --git a/b2g/chrome/content/screen.js b/b2g/chrome/content/screen.js
index f20f65797643..1f5eb8266737 100644
--- a/b2g/chrome/content/screen.js
+++ b/b2g/chrome/content/screen.js
@@ -57,12 +57,19 @@ window.addEventListener('ContentStart', function() {
   };
 
   // Get the command line arguments that were passed to the b2g client
-  let args = window.arguments[0].QueryInterface(Ci.nsICommandLine);
-  let screenarg;
+  let args;
+  try {
+    // On Firefox Mulet, we don't always have a command line argument
+    args = window.arguments[0].QueryInterface(Ci.nsICommandLine);
+  } catch(e) {}
+
+  let screenarg = null;
 
   // Get the --screen argument from the command line
   try {
-    screenarg = args.handleFlagWithParam('screen', false);
+    if (args) {
+      screenarg = args.handleFlagWithParam('screen', false);
+    }
 
     // If there isn't one, use the default screen
     if (screenarg === null)