For #14552: Do not display back button when there is no tab history.

app/src/main/assets/high_risk_error_pages.html

@@ -34,4 +34,9 @@
   </body>
 
   <script src="./errorPageScripts.js"></script>
+  <script type="text/javascript">
+    if (window.history.length == 1) {
+        document.getElementById('backButton').style.display = 'none';
+    }
+  </script>
 </html>

app/src/main/assets/low_and_medium_risk_error_pages.html

@@ -71,6 +71,10 @@
   </body>
 
   <script type="text/javascript">
+    if (window.history.length == 1) {
+        document.getElementById('advancedPanelBackButton').style.display = 'none';
+    }
+
     function toggleAdvancedAndScroll() {
       toggleAdvanced();