--- a/devtools/client/shared/widgets/Tooltip.js
+++ b/devtools/client/shared/widgets/Tooltip.js
@@ -640,16 +640,17 @@ Tooltip.prototype = {
     let def = promise.defer();
 
     // Create an iframe
     let iframe = this.doc.createElementNS(XHTML_NS, "iframe");
     iframe.setAttribute("transparent", true);
     iframe.setAttribute("width", width);
     iframe.setAttribute("height", height);
     iframe.setAttribute("flex", "1");
+    iframe.setAttribute("tooltip", "aHTMLTooltip");
     iframe.setAttribute("class", "devtools-tooltip-iframe");
 
     // Wait for the load to initialize the widget
     function onLoad() {
       iframe.removeEventListener("load", onLoad, true);
       def.resolve(iframe);
     }
     iframe.addEventListener("load", onLoad, true);