--- a/testing/marionette/components/marionette.js
+++ b/testing/marionette/components/marionette.js
@@ -154,16 +154,18 @@ MarionetteComponent.prototype = {
 MarionetteComponent.prototype.handle = function(cmdLine) {
   if (!this.enabled && cmdLine.handleFlag("marionette", false)) {
     this.enabled = true;
     this.logger.info("Enabled via --marionette");
   }
 };
 
 MarionetteComponent.prototype.observe = function(subject, topic, data) {
+  this.logger.debug(`Received observer notification "${topic}"`);
+
   switch (topic) {
     case "command-line-startup":
       Services.obs.removeObserver(this, topic);
       this.handle(subject);
 
     case "profile-after-change":
       // Using sessionstore-windows-restored as the xpcom category doesn't
       // seem to work, so we wait for that by adding an observer here.