diff --git a/browser/devtools/responsivedesign/responsivedesign.jsm b/browser/devtools/responsivedesign/responsivedesign.jsm
index 5a3191bd866..a8c6953599c 100644
--- a/browser/devtools/responsivedesign/responsivedesign.jsm
+++ b/browser/devtools/responsivedesign/responsivedesign.jsm
@@ -238,7 +238,10 @@ ResponsiveUI.prototype = {
      }
    },
 
-   onPageUnload: function() {
+   onPageUnload: function(evt) {
+     // Ignore sub frames unload events
+     if (evt.target != this.browser.contentDocument)
+       return;
      if (this.closing)
        return;
      if (this.touchEventHandler) {