--- a/mobile/android/chrome/content/WebAppRT.js
+++ b/mobile/android/chrome/content/WebAppRT.js
@@ -62,17 +62,19 @@ let WebAppRT = {
         if (aManifest) {
           PermissionsInstaller.installPermissions(aApp, true);
         }
       });
     }
 
 #ifdef MOZ_ANDROID_SYNTHAPKS
     // If the app is in debug mode, configure and enable the remote debugger.
-    if (sendMessageToJava({ type: "NativeApp:IsDebuggable" })) {
+    // sendMessageToJava can only return string values, so it returns the string
+    // "true" rather than boolean true if the app is in debug mode.
+    if (sendMessageToJava({ type: "NativeApp:IsDebuggable" }) === "true") {
       this._enableRemoteDebugger(aUrl);
     }
 #endif
 
     this.findManifestUrlFor(aUrl, aCallback);
   },
 
   getManifestFor: function (aUrl, aCallback) {