--- a/testing/marionette/frame.js
+++ b/testing/marionette/frame.js
@@ -11,19 +11,16 @@ Cu.import("resource://gre/modules/XPCOMU
 
 this.EXPORTED_SYMBOLS = ["frame"];
 
 /** @namespace */
 this.frame = {};
 
 const FRAME_SCRIPT = "chrome://marionette/content/listener.js";
 
-// list of OOP frames that has the frame script loaded
-var remoteFrames = [];
-
 /**
  * An object representing a frame that Marionette has loaded a
  * frame script in.
  */
 frame.RemoteFrame = function(windowId, frameId) {
   // outerWindowId relative to main process
   this.windowId = windowId;
   // actual frame relative to the windowId's frames list
@@ -146,24 +143,24 @@ frame.Manager = class {
    * a list of remote frames.
    */
   switchToFrame(winId, frameId) {
     let oopFrame = this.getOopFrame(winId, frameId);
     let mm = this.getFrameMM(winId, frameId);
 
     // see if this frame already has our frame script loaded in it;
     // if so, just wake it up
-    for (let i = 0; i < remoteFrames.length; i++) {
-      let f = remoteFrames[i];
+    for (let i = 0; i < this.remoteFrames.length; i++) {
+      let f = this.remoteFrames[i];
       let fmm = f.messageManager.get();
       try {
         fmm.sendAsyncMessage("aliveCheck", {});
       } catch (e) {
         if (e.result == Cr.NS_ERROR_NOT_INITIALIZED) {
-          remoteFrames.splice(i--, 1);
+          this.remoteFrames.splice(i--, 1);
           continue;
         }
       }
 
       if (fmm == mm) {
         this.currentRemoteFrame = f;
         this.addMessageManagerListeners(mm);
 
@@ -173,17 +170,17 @@ frame.Manager = class {
     }
 
     // if we get here, then we need to load the frame script in this frame,
     // and set the frame's ChromeMessageSender as the active message manager
     // the driver will listen to.
     this.addMessageManagerListeners(mm);
     let f = new frame.RemoteFrame(winId, frameId);
     f.messageManager = Cu.getWeakReference(mm);
-    remoteFrames.push(f);
+    this.remoteFrames.push(f);
     this.currentRemoteFrame = f;
 
     mm.loadFrameScript(FRAME_SCRIPT, true, true);
 
     return oopFrame.id;
   }
 
   /*