Index: polyfill.js
===================================================================
--- a/polyfill.js
+++ b/polyfill.js
@@ -107,27 +107,16 @@
     // If the property is not writable assigning it will fail, so we use
     // Object.defineProperty here instead. Assuming the property isn't
     // inherited its other attributes (e.g. enumerable) are preserved,
     // except for accessor attributes (e.g. get and set) which are discarded
     // since we're specifying a value.
     Object.defineProperty(object, name, {
       value(...args)
       {
-        if (typeof args[args.length - 1] == "function")
-          return func.apply(object, args);
-
-        // If the last argument is undefined, we drop it from the list assuming
-        // it stands for the optional callback. We must do this, because we have
-        // to replace it with our own callback. If we simply append our own
-        // callback to the list, it won't match the signature of the function
-        // and will cause an exception.
-        if (typeof args[args.length - 1] == "undefined")
-          args.pop();
-
         let resolvePromise = null;
         let rejectPromise = null;
 
         func.call(object, ...args, result =>
         {
           let error = browser.runtime.lastError;
           if (error && !portClosedBeforeResponseError.test(error.message))
           {