--- a/browser/devtools/inspector/inspector-panel.js
+++ b/browser/devtools/inspector/inspector-panel.js
@@ -630,34 +630,38 @@ InspectorPanel.prototype = {
   /**
    * Copy the innerHTML of the selected Node to the clipboard.
    */
   copyInnerHTML: function InspectorPanel_copyInnerHTML()
   {
     if (!this.selection.isNode()) {
       return;
     }
-    let toCopy = this.selection.node.innerHTML;
-    if (toCopy) {
-      clipboardHelper.copyString(toCopy);
-    }
+    this._copyLongStr(this.walker.innerHTML(this.selection.nodeFront));
   },
 
   /**
    * Copy the outerHTML of the selected Node to the clipboard.
    */
   copyOuterHTML: function InspectorPanel_copyOuterHTML()
   {
     if (!this.selection.isNode()) {
       return;
     }
-    let toCopy = this.selection.node.outerHTML;
-    if (toCopy) {
-      clipboardHelper.copyString(toCopy);
-    }
+
+    this._copyLongStr(this.walker.outerHTML(this.selection.nodeFront));
+  },
+
+  _copyLongStr: function(promise) {
+    return promise.then(longstr => {
+      return longstr.string().then(toCopy => {
+        longstr.release().then(null, console.error);
+        clipboardHelper.copyString(toCopy);
+      });
+    }).then(null, console.error);
   },
 
   /**
    * Copy a unique selector of the selected Node to the clipboard.
    */
   copyUniqueSelector: function InspectorPanel_copyUniqueSelector()
   {
     if (!this.selection.isNode()) {