--- a/testing/marionette/event.js
+++ b/testing/marionette/event.js
@@ -1384,16 +1384,25 @@ event.focus = function(el, opts = {}) {
   let doc = el.ownerDocument || el.document;
   let win = doc.defaultView;
 
   let ev = new win.FocusEvent(el);
   ev.initEvent("focus", opts.canBubble, true);
   el.dispatchEvent(ev);
 };
 
+event.blur = function(el, {canBubble = true} = {}) {
+  let doc = el.ownerDocument || el.document;
+  let win = doc.defaultView;
+
+  let ev = new win.FocusEvent(el);
+  ev.initEvent("blur", canBubble, true);
+  el.dispatchEvent(ev);
+};
+
 event.mouseover = function(el, modifiers = {}, opts = {}) {
   return event.sendEvent("mouseover", el, modifiers, opts);
 };
 
 event.mousemove = function(el, modifiers = {}, opts = {}) {
   return event.sendEvent("mousemove", el, modifiers, opts);
 };