diff --git a/web/hand_tool.js b/web/hand_tool.js
index 987e11d1f..cd4b3054a 100644
--- a/web/hand_tool.js
+++ b/web/hand_tool.js
@@ -25,6 +25,9 @@ var HandTool = {
     this.handTool = new GrabToPan({
       element: options.container,
       onActiveChanged: function(isActive) {
+        if (!toggleHandTool) {
+          return;
+        }
         if (isActive) {
           toggleHandTool.title =
             mozL10n.get('hand_tool_disable.title', null, 'Disable hand tool');
@@ -36,9 +39,11 @@ var HandTool = {
           toggleHandTool.firstElementChild.textContent =
             mozL10n.get('hand_tool_enable_label', null, 'Enable hand tool');
         }
-    }
+      }
     });
-    toggleHandTool.addEventListener('click', this.handTool.toggle, false);
+    if (toggleHandTool) {
+      toggleHandTool.addEventListener('click', this.handTool.toggle, false);
+    }
     // TODO: Read global prefs and call this.handTool.activate() if needed.
   },
 
diff --git a/web/secondary_toolbar.js b/web/secondary_toolbar.js
index aff0c2b75..c9375823d 100644
--- a/web/secondary_toolbar.js
+++ b/web/secondary_toolbar.js
@@ -41,7 +41,10 @@ var SecondaryToolbar = {
 
     // Attach the event listeners.
     var elements = [
+      // Button to toggle the visibility of the secondary toolbar:
       { element: this.toggleButton, handler: this.toggle },
+      // All items within the secondary toolbar
+      // (except for toggleHandTool, hand_tool.js is responsible for it):
       { element: this.presentationModeButton,
         handler: this.presentationModeClick },
       { element: this.openFile, handler: this.openFileClick },