Fixed an error on FireFox with the tab selection for Graph section

Author: Kidel

index.html

@@ -45,8 +45,8 @@ <h4><a href="https://github.com/Kidel/Netkit-Lab-Generator" target="_blank">http
     <div class="col-xs-1">
         <!-- Nav tabs -->
         <ul class="nav nav-tabs tabs-left">
-            <li id="tab-home" class="tab-label active"><a href="#home" data-toggle="tab" onclick="toggle_tab(this)">Home</a></li>
-            <li id="tab-graph" class="tab-label"><a href="#graph" data-toggle="tab" onclick="toggle_tab(this)">Graph</a></li>
+            <li id="tab-home" class="tab-label active"><a href="#home" data-toggle="tab" onclick="toggle_tab(event, this)">Home</a></li>
+            <li id="tab-graph" class="tab-label"><a href="#graph" data-toggle="tab" onclick="toggle_tab(event, this)">Graph</a></li>
         </ul>
     </div>
     <div class="col-xs-10">

js/page.js

@@ -1,4 +1,4 @@
-function toggle_tab(elem) {
+function toggle_tab(event, elem) {
     event.preventDefault();
     var elems = document.getElementsByClassName("tab-pane");
     for(var j in elems) {