diff --git a/app/app.js b/app/app.js
index 7f8cc78..2ba59b4 100644
--- a/app/app.js
+++ b/app/app.js
@@ -130,57 +130,61 @@ app.directive('spChallenge', function($compile, UserFactory) {
                 // Set up an iframe to run code in
                 var iframe = $('<iframe>');
                 $('body').append(iframe);
-                iframe.contents().find('body').append(assignment.html);
                 var frameWindow = iframe[0].contentWindow;
 
-                if(assignment.prepare) {
-                    assignment.prepare(frameWindow);
-                }
+                var interval = setInterval(() => {
+                    if(frameWindow.document.readyState === 'complete') {
+                        clearInterval(interval);
 
-                // Load jQuery
-                if(assignment.jquery) {
-                    var jquerySource = '';
-                    var f = $.ajax('static/js/jquery.js', {
-                        async: false,
-                        cache: true,
-                        success: function(data) {
-                            jquerySource = data;
-                        }
-                    });
-                    frameWindow.eval(jquerySource);
-                }
+                        iframe.contents().find('body').append(assignment.html);
 
-                try {
-
-                    // Run the code!
-                    frameWindow.eval(user_code);
-
-                    // Test the return value
-                    var returnValue = frameWindow.eval(assignment.return);
-                    assignment.tester(returnValue, user_code);
-
-                    // No error, complete the assignment!
-                    UserFactory.completeAssignment(assignment.id, assignment.points);
-
-                    $scope.completed = true;
-                    $scope.element.find('.live_assignment').addClass('completed');
-                    $scope.element.find('.complete')
-                        .slideDown()
-                        .delay(1000)
-                        .slideUp();
-
-                } catch(e) {
-                    // Show error to user
-                    $scope.element.find('.error').html("Error: " + e)
-                        .slideDown()
-                        .delay(3000)
-                        .slideUp();
-                } finally {
-                    iframe.remove();
-                }
-			}
+                        if(assignment.prepare) {
+                            assignment.prepare(frameWindow);
+                        }
 
+                        // Load jQuery
+                        if(assignment.jquery) {
+                            var jquerySource = '';
+                            var f = $.ajax('static/js/jquery.js', {
+                                async: false,
+                                cache: true,
+                                success: function(data) {
+                                    jquerySource = data;
+                                }
+                            });
+                            frameWindow.eval(jquerySource);
+                        }
 
+                        try {
+                            // Run the code!
+                            frameWindow.eval(user_code);
+
+                            // Test the return value
+                            var returnValue = frameWindow.eval(assignment.return);
+                            assignment.tester(returnValue, user_code);
+
+                            // No error, complete the assignment!
+                            UserFactory.completeAssignment(assignment.id, assignment.points);
+
+                            $scope.completed = true;
+                            $scope.element.find('.live_assignment').addClass('completed');
+                            $scope.element.find('.complete')
+                                .slideDown()
+                                .delay(1000)
+                                .slideUp();
+
+                        } catch(e) {
+                            // Show error to user
+                            $scope.element.find('.error').html("Error: " + e)
+                                .slideDown()
+                                .delay(3000)
+                                .slideUp();
+                        } finally {
+                            iframe.remove();
+                        }
+                    }
+                }, 50);
+			}
 		}
 	};
 });
diff --git a/jquery/opdrachten.html b/jquery/opdrachten.html
index fb376fd..adbcdf0 100644
--- a/jquery/opdrachten.html
+++ b/jquery/opdrachten.html
@@ -9,8 +9,6 @@ <h1>Opdrachten week 2</h1>
 
   <p>Welkom terug bij week 2! Deze week gaan we oefenen met jQuery, één van de meest populaire JavaScript libraries. In de presentatie van deze week en vorige week staan alle voorbeelden die je nodig hebt om de opdrachten te maken.</p>
 
-  <p><em>Onderstaande challenges kan je helaas niet maken met Firefox</em></p>
-
   <sp-challenge assignment="jquery_changecolor"></sp-challenge>
   <sp-challenge assignment="jquery_hide"></sp-challenge>
   <sp-challenge assignment="jquery_delegated"></sp-challenge>