--- a/browser/devtools/styleinspector/rule-view.js
+++ b/browser/devtools/styleinspector/rule-view.js
@@ -1036,17 +1036,19 @@ CssRuleView.prototype = {
 
     this.element.removeEventListener("copy", this._boundCopy);
     delete this._boundCopy;
 
     if (this.element.parentNode) {
       this.element.parentNode.removeChild(this.element);
     }
 
-    this.elementStyle.destroy();
+    if (this.elementStyle) {
+      this.elementStyle.destroy();
+    }
 
     this.popup.destroy();
   },
 
   /**
    * Update the highlighted element.
    *
    * @param {nsIDOMElement} aElement