--- a/browser/devtools/shared/event-emitter.js
+++ b/browser/devtools/shared/event-emitter.js
@@ -57,16 +57,17 @@ EventEmitter.prototype = {
    * @param function aListener
    *        Called when the event is fired.  Will be called at most one time.
    */
   once: function EventEmitter_once(aEvent, aListener) {
     let handler = function() {
       this.off(aEvent, handler);
       aListener.apply(null, arguments);
     }.bind(this);
+    handler._originalListener = aListener;
     this.on(aEvent, handler);
   },
 
   /**
    * Remove a previously-registered event listener.  Works for events
    * registered with either on or once.
    *
    * @param string aEvent
@@ -74,17 +75,19 @@ EventEmitter.prototype = {
    * @param function aListener
    *        The listener to remove.
    */
   off: function EventEmitter_off(aEvent, aListener) {
     if (!this._eventEmitterListeners)
       return;
     let listeners = this._eventEmitterListeners.get(aEvent);
     if (listeners) {
-      this._eventEmitterListeners.set(aEvent, listeners.filter(function(l) aListener != l));
+      this._eventEmitterListeners.set(aEvent, listeners.filter(l => {
+        return l !== aListener && l._originalListener !== aListener;
+      }));
     }
   },
 
   /**
    * Emit an event.  All arguments to this method will
    * be sent to listner functions.
    */
   emit: function EventEmitter_emit(aEvent) {

--- a/browser/devtools/shared/test/browser_eventemitter_basic.js
+++ b/browser/devtools/shared/test/browser_eventemitter_basic.js
@@ -69,12 +69,29 @@ function testEmitter(aObject) {
 
     emitter.on("tick", c1);
     emitter.on("tick", c2);
     emitter.on("tick", c3);
     emitter.on("tick", c4);
 
     emitter.emit("tick");
 
+    offAfterOnce();
+  }
+
+  function offAfterOnce() {
+    let enteredC1 = false;
+
+    function c1() {
+      enteredC1 = true;
+    }
+
+    emitter.once("oao", c1);
+    emitter.off("oao", c1);
+
+    emitter.emit("oao");
+
+    ok(!enteredC1, "c1 should not be called");
+
     delete emitter;
     finish();
   }
 }