--- a/devtools/server/actors/highlighters/simple-outline.js
+++ b/devtools/server/actors/highlighters/simple-outline.js
@@ -1,16 +1,20 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 "use strict";
 
-const { installHelperSheet,
-  addPseudoClassLock, removePseudoClassLock } = require("./utils/markup");
+const {
+  installHelperSheet,
+  isNodeValid,
+  addPseudoClassLock,
+  removePseudoClassLock
+} = require("./utils/markup");
 
 // SimpleOutlineHighlighter's stylesheet
 const HIGHLIGHTED_PSEUDO_CLASS = ":-moz-devtools-highlighted";
 const SIMPLE_OUTLINE_SHEET = `.__fx-devtools-hide-shortcut__ {
                                 visibility: hidden !important
                               }
                               ${HIGHLIGHTED_PSEUDO_CLASS} {
                                 outline: 2px dashed #F06!important;
@@ -36,17 +40,17 @@ SimpleOutlineHighlighter.prototype = {
     this.chromeDoc = null;
   },
 
   /**
    * Show the highlighter on a given node
    * @param {DOMNode} node
    */
   show: function (node) {
-    if (!this.currentNode || node !== this.currentNode) {
+    if (isNodeValid(node) && (!this.currentNode || node !== this.currentNode)) {
       this.hide();
       this.currentNode = node;
       installHelperSheet(node.ownerDocument.defaultView, SIMPLE_OUTLINE_SHEET);
       addPseudoClassLock(node, HIGHLIGHTED_PSEUDO_CLASS);
     }
     return true;
   },