diff --git a/src/test/html/content/harness.js b/src/test/html/content/harness.js
index 725380838c2..0697376df4f 100644
--- a/src/test/html/content/harness.js
+++ b/src/test/html/content/harness.js
@@ -12,16 +12,28 @@ function _pass(s, m) {
   window.alert(_oneline("TEST-PASS | " + s + ": " + m));
 }
 
-function is(a, b, c) {
-  let f = a != b ? _fail : _pass;
-  let m = !c ? "" : c;
-  f(a + " == " + b, m);
+function _printer(opstr, op) {
+  return function (a, b, msg) {
+    let f = op(a,b) ? _pass : _fail;
+    if (!msg) msg = "";
+    f(a + " " + opstr + " " + b, msg);
+  };
 }
 
-function isnot(a, b, c) {
-  let f = (a != b) ? _pass : _fail;
-  let m = !c ? "" : c;
-  f(a + " != " + b, m);
+var is          = _printer("==",           function (a,b) { return a == b; });
+var is_a        = _printer("is a",         function (a,b) { return a instanceof b; });
+var is_in       = _printer("is in",        function (a,b) { return a in b; });
+var is_not_in   = _printer("is not in",    function (a,b) { return !(a in b); });
+var as_str_is   = _printer("as string is", function (a,b) { return String(a) == b; });
+var isnot       = _printer("!=",           function (a,b) { return a != b; });
+var lt          = _printer("<",            function (a,b) { return a <  b; });
+var gt          = _printer(">",            function (a,b) { return a >  b; });
+var leq         = _printer("<=",           function (a,b) { return a <= b; });
+var geq         = _printer(">=",           function (a,b) { return a >= b; });
+var starts_with = _printer("starts with",  function (a,b) { return a.indexOf(b) == 0; });
+
+function is_function(val, name) {
+  starts_with(String(val), "function " + name + "(");
 }
 
 var _test_complete = false;
diff --git a/src/test/html/content/test_childnodes.html b/src/test/html/content/test_childnodes.html
index f8a4d9797c6..205a6124959 100644
--- a/src/test/html/content/test_childnodes.html
+++ b/src/test/html/content/test_childnodes.html
@@ -18,11 +18,11 @@
     var child2 = document.createElement("p");
     elem.appendChild(child2);
 
-    is(1 in children, true);
+    is_in(1, children);
     is(children.length, 2);
     is(children.item(1), child2);
 
-    is(!(2 in children), true);
+    is_not_in(2, children);
     is(children.item(2), null);
 
     finish();
diff --git a/src/test/html/content/test_create_element.html b/src/test/html/content/test_create_element.html
index eaa3e11377a..f62c599504d 100644
--- a/src/test/html/content/test_create_element.html
+++ b/src/test/html/content/test_create_element.html
@@ -8,11 +8,11 @@
     var elem = document.createElement("foo");
     is(elem.tagName, "FOO");
     var elem = document.createElement("p");
-    is(elem instanceof HTMLParagraphElement, true);
+    is_a(elem, HTMLParagraphElement);
     var elem = document.createElement("sPAn");
-    is(elem instanceof HTMLSpanElement, true);
+    is_a(elem, HTMLSpanElement);
     var text = document.createTextNode("hello");
-    is(text instanceof Text, true);
+    is_a(text, Text);
     finish();
   </script>
 </body>
diff --git a/src/test/html/content/test_document_getElementById.html b/src/test/html/content/test_document_getElementById.html
index 20140274477..370ec77fde0 100644
--- a/src/test/html/content/test_document_getElementById.html
+++ b/src/test/html/content/test_document_getElementById.html
@@ -13,12 +13,12 @@
       let foo = document.getElementById("foo");
       isnot(foo, null, "test-1-0, on static page");
       is(foo && foo.tagName, "HEAD", "test1-1, on static page");
-      is(foo instanceof HTMLHeadElement, true, "test1-2, on static page");
+      is_a(foo, HTMLHeadElement, "test1-2, on static page");
 
       let bar = document.getElementById("bar");
       isnot(bar, null, "test1-3, on static page");
       is(bar && bar.tagName, "DIV", "test1-4, on static page");
-      is(bar instanceof HTMLDivElement, true, "test1-5, on static page");
+      is_a(bar, HTMLDivElement, "test1-5, on static page");
     }
 
     // test2: scripted element
@@ -32,7 +32,7 @@
       let appended = document.getElementById(TEST_ID);
       isnot(appended, null, "test2-0, appended element");
       is(appended && appended.tagName, "DIV", "test2-1, appended element");
-      is(appended instanceof HTMLDivElement, true, "test2-2, appended element");
+      is_a(appended, HTMLDivElement, "test2-2, appended element");
 
       // test: removed element
       gBody.removeChild(test);
diff --git a/src/test/html/content/test_empty_clientrect.html b/src/test/html/content/test_empty_clientrect.html
index 3902886ee99..3671ca5bcc4 100644
--- a/src/test/html/content/test_empty_clientrect.html
+++ b/src/test/html/content/test_empty_clientrect.html
@@ -4,14 +4,14 @@
 <script>
 var rect = window.document.head.getBoundingClientRect();
 var rects = window.document.head.getClientRects();
-is(rect instanceof ClientRect, true);
+is_a(rect, ClientRect);
 is(rect.top, 0);
 is(rect.bottom, 0);
 is(rect.left, 0);
 is(rect.right, 0);
 is(rect.width, 0);
 is(rect.height, 0);
-is(rects instanceof ClientRectList, true);
+is_a(rects, ClientRectList);
 is(rects.length, 0);
 finish();
 </script>
diff --git a/src/test/html/content/test_navigator.html b/src/test/html/content/test_navigator.html
index 7d786ea8ec6..c7809f36895 100644
--- a/src/test/html/content/test_navigator.html
+++ b/src/test/html/content/test_navigator.html
@@ -6,7 +6,7 @@
 <body>
 <script>
 is(window.navigator, window.navigator);
-is(String(window.navigator), '[object Navigator]');
+is_a(window.navigator, Navigator);
 
 var nav = window.navigator;
 is(nav.doNotTrack, "unspecified");
diff --git a/src/test/html/content/test_prototypes.html b/src/test/html/content/test_prototypes.html
index 9eb3e878e31..61835bd750e 100644
--- a/src/test/html/content/test_prototypes.html
+++ b/src/test/html/content/test_prototypes.html
@@ -5,14 +5,14 @@
 <body>
   <foo-á>foo</foo-á>
 <script>
-is(window.document.documentElement instanceof Node, true);
-is(window.document.documentElement instanceof Element, true);
-is(window.document.documentElement instanceof HTMLElement, true);
-is(window.document.documentElement instanceof HTMLHtmlElement, true);
-is(window.document instanceof Document, true);
-is(window.document instanceof HTMLDocument, true);
+is_a(window.document.documentElement, Node);
+is_a(window.document.documentElement, Element);
+is_a(window.document.documentElement, HTMLElement);
+is_a(window.document.documentElement, HTMLHtmlElement);
+is_a(window.document, Document);
+is_a(window.document, HTMLDocument);
 is(window.document.documentElement.tagName, "HTML");
-is(window.document.getElementsByTagName('foo-á')[0] instanceof HTMLUnknownElement, true);
+is_a(window.document.getElementsByTagName('foo-á')[0], HTMLUnknownElement);
 is(window.document.getElementsByTagName('foo-á')[0].tagName, "FOO-á");
 finish();
 </script>