--- a/toolkit/modules/addons/WebRequest.jsm
+++ b/toolkit/modules/addons/WebRequest.jsm
@@ -808,24 +808,24 @@ HttpObserverManager = {
 
   examine(channel, topic, data) {
     let loadContext = this.getLoadContext(channel);
 
     if (this.needTracing) {
       // Check whether we've already added a listener to this channel,
       // so we don't wind up chaining multiple listeners.
       let channelData = getData(channel);
-      if (!channelData.listener && channel instanceof Ci.nsITraceableChannel) {
+      if (!channelData.hasListener && channel instanceof Ci.nsITraceableChannel) {
         let responseStatus = channel.responseStatus;
         // skip redirections, https://bugzilla.mozilla.org/show_bug.cgi?id=728901#c8
         if (responseStatus < 300 || responseStatus >= 400) {
           let listener = new StartStopListener(this, loadContext);
           let orig = channel.setNewListener(listener);
           listener.orig = orig;
-          channelData.listener = listener;
+          channelData.hasListener = true;
         }
       }
     }
 
     this.runChannelListener(channel, loadContext, "headersReceived");
   },
 
   onChannelReplaced(oldChannel, newChannel) {