--- a/browser/devtools/inspector/inspector-panel.js
+++ b/browser/devtools/inspector/inspector-panel.js
@@ -179,28 +179,34 @@ InspectorPanel.prototype = {
   markDirty: function InspectorPanel_markDirty() {
     this.isDirty = true;
   },
 
   /**
    * Hooks the searchbar to show result and auto completion suggestions.
    */
   setupSearchBox: function InspectorPanel_setupSearchBox() {
+    let searchDoc;
+    if (this.target.isLocalTab) {
+      searchDoc = this.browser.contentDocument;
+    } else if (this.target.window) {
+      searchDoc = this.target.window.document;
+    } else {
+      return;
+    }
     // Initiate the selectors search object.
     let setNodeFunction = function(node) {
       this.selection.setNode(node, "selectorsearch");
     }.bind(this);
     if (this.searchSuggestions) {
       this.searchSuggestions.destroy();
       this.searchSuggestions = null;
     }
     this.searchBox = this.panelDoc.getElementById("inspector-searchbox");
-    this.searchSuggestions = new SelectorSearch(this.browser.contentDocument,
-                                                this.searchBox,
-                                                setNodeFunction);
+    this.searchSuggestions = new SelectorSearch(searchDoc, this.searchBox, setNodeFunction);
   },
 
   /**
    * Build the sidebar.
    */
   setupSidebar: function InspectorPanel_setupSidebar() {
     let tabbox = this.panelDoc.querySelector("#inspector-sidebar");
     this.sidebar = new ToolSidebar(tabbox, this);