diff --git a/tests/resources/testharness.js b/tests/resources/testharness.js
--- a/tests/resources/testharness.js
+++ b/tests/resources/testharness.js
@@ -1323,58 +1323,76 @@ policies and contribution forms [3].
                                         }
                                         i++;
                                     }
                                     return rv;
                                 }];

         log.appendChild(render(summary_template, {num_tests:tests.length}, output_document));

+        function hide_result_class(result_class)
+        {
+            var style_element = output_document.createElementNS(xhtml_ns, "style");
+            style_element.id = "hide-" + result_class;
+            style_element.innerHTML = "table#results > tbody > tr."+result_class+"{display:none}";
+            output_document.body.appendChild(style_element);
+        }
+
         forEach(output_document.querySelectorAll("section#summary label"),
                 function(element)
                 {
                     on_event(element, "click",
                              function(e)
                              {
                                  if (output_document.getElementById("results") === null)
                                  {
                                      e.preventDefault();
                                      return;
                                  }
                                  var result_class = element.parentNode.getAttribute("class");
                                  var style_element = output_document.querySelector("style#hide-" + result_class);
                                  var input_element = element.querySelector("input");
                                  if (!style_element && !input_element.checked) {
-                                     style_element = output_document.createElementNS(xhtml_ns, "style");
-                                     style_element.id = "hide-" + result_class;
-                                     style_element.innerHTML = "table#results > tbody > tr."+result_class+"{display:none}";
-                                     output_document.body.appendChild(style_element);
+                                     hide_result_class(result_class);
                                  } else if (style_element && input_element.checked) {
                                      style_element.parentNode.removeChild(style_element);
                                  }
                              });
                 });

+        if (tests.length > 1000) {
+            // Hide all the results by default so that it renders more quickly
+            forEach(output_document.querySelectorAll("section#summary label"),
+                    function(element)
+                    {
+                        element.querySelector("input").checked = false;
+                        hide_result_class(element.parentNode.className);
+                    });
+        }
+
+        // This use of innerHTML plus manual escaping is not recommended in
+        // general, but is necessary here for performance.  Using textContent
+        // on each individual <td> adds tens of seconds of execution time for
+        // large test suites (tens of thousands of tests).
         log.appendChild(document.createElement("section"));
         var html = "<h2>Details</h2><table id=results>"
             + "<thead><tr><th>Result</th><th>Test Name</th><th>Message</th></tr></thead>"
             + "<tbody>";
         for (var i = 0; i < tests.length; i++) {
-            html += "<tr><td></td><td></td><td></td></tr>";
+            html += '<tr class="'
+                + status_class(status_text[tests[i].status])
+                + '"><td>'
+                + status_text[tests[i].status]
+                + "</td><td>"
+                + tests[i].name.replace(/\&/g, "&amp;").replace(/</g, "&lt;")
+                + "</td><td>"
+                + (tests[i].message ? tests[i].message.replace(/\&/g, "&amp;").replace(/</g, "&lt;") : " ")
+                + "</td></tr>";
         }
         log.lastChild.innerHTML = html + "</tbody></table>";
-        var tbody = log.querySelector("tbody");
-        for (var i = 0; i < tests.length; i++)
-        {
-            var tr = tbody.childNodes[i];
-            tr.className = status_class(status_text[tests[i].status]);
-            tr.childNodes[0].textContent = status_text[tests[i].status];
-            tr.childNodes[1].textContent = tests[i].name;
-            tr.childNodes[2].textContent = tests[i].message ? tests[i].message : " ";
-        }
     };

     var output = new Output();
     add_start_callback(function (properties) {output.setup(properties);});
     add_result_callback(function (test) {output.show_status(tests);});
     add_completion_callback(function (tests, harness_status) {output.show_results(tests, harness_status);});

     /*