--- a/testing/marionette/components/marionette.js
+++ b/testing/marionette/components/marionette.js
@@ -286,17 +286,17 @@ class MarionetteMainProcess {
     this.enabled = env.exists(ENV_ENABLED);
     this.alteredPrefs = new Set();
 
     Services.prefs.addObserver(PREF_ENABLED, this);
     Services.ppmm.addMessageListener("Marionette:IsRunning", this);
   }
 
   get running() {
-    return this.server && this.server.alive;
+    return !!this.server && this.server.alive;
   }
 
   set enabled(value) {
     MarionettePrefs.enabled = value;
   }
 
   get enabled() {
     return MarionettePrefs.enabled;