Fixed credit form submission bug

Firefox requires the form to be attached to a DOM element

ECOM-2492

lms/static/js/commerce/credit.js

@@ -23,6 +23,7 @@ var edx = edx || {};
             context: this,
             success: function (requestData) {
                 var $form = $('<form>', {
+                    'class': 'hidden',
                     'action': requestData.url,
                     'method': 'POST',
                     'accept-method': 'UTF-8'
@@ -35,7 +36,7 @@ var edx = edx || {};
                     }).appendTo($form);
                 });
 
-                $form.submit();
+                $form.appendTo('body').submit();
             }
         });
     };

lms/static/js/commerce/views/receipt_view.js

@@ -288,6 +288,8 @@ function completeOrder(event) {     // jshint ignore:line
         providerId = $(event).data("provider"),
         $errorContainer = $("#error-container");
 
+    event.preventDefault();
+
     analytics.track(
         "edx.bi.credit.clicked_complete_credit",
         {

lms/static/js/dashboard/credit.js

@@ -36,6 +36,8 @@ var edx = edx || {};
                 username = $target.data("user"),
                 providerId = $target.data("provider");
 
+            event.preventDefault();
+
             edx.commerce.credit.createCreditRequest(providerId, courseKey, username).fail(function () {
                 $(".credit-action").hide();
                 $errorContainer.toggleClass("is-hidden");