diff --git a/common/content/buffer.js b/common/content/buffer.js
index 5c2f0c97..9e8b565c 100644
--- a/common/content/buffer.js
+++ b/common/content/buffer.js
@@ -1217,6 +1217,13 @@ var Buffer = Module("buffer", {
         return elem || doc.body || doc.documentElement;
     },
 
+    scrollTo: function scrollTo(elem, left, top) {
+        if (left != null)
+            elem.scrollLeft = left;
+        if (top != null)
+            elem.scrollTop = top;
+    },
+
     scrollVertical: function scrollVertical(elem, increment, number) {
         elem = elem || Buffer.findScrollable(number, false);
         let fontSize = parseInt(util.computedStyle(elem).fontSize);
@@ -1227,10 +1234,8 @@ var Buffer = Module("buffer", {
         else
             throw Error();
 
-        if (number < 0 ? elem.scrollTop > 0 : elem.scrollTop < elem.scrollHeight - elem.clientHeight)
-            elem.scrollTop += number * increment;
-        else
-            dactyl.beep();
+        dactyl.assert(number < 0 ? elem.scrollTop > 0 : elem.scrollTop < elem.scrollHeight - elem.clientHeight);
+        Buffer.scrollTo(elem, null, elem.scrollTop + number * increment);
     },
 
     scrollHorizontal: function scrollHorizontal(elem, increment, number) {
@@ -1243,21 +1248,19 @@ var Buffer = Module("buffer", {
         else
             throw Error();
 
-        if (number < 0 ? elem.scrollLeft > 0 : elem.scrollLeft < elem.scrollWidth - elem.clientWidth)
-            elem.scrollLeft += number * increment;
-        else
-            dactyl.beep();
+        dactyl.assert(number < 0 ? elem.scrollLeft > 0 : elem.scrollLeft < elem.scrollWidth - elem.clientWidth);
+        Buffer.scrollTo(elem, elem.scrollLeft + number * increment, null);
     },
 
     scrollToPercent: function scrollElemToPercent(elem, horizontal, vertical) {
         elem = elem || Buffer.findScrollable(0, vertical == null);
         marks.add("'", true);
 
-        if (horizontal != null)
-            elem.scrollLeft = (elem.scrollWidth - elem.clientWidth) * (horizontal / 100);
-
-        if (vertical != null)
-            elem.scrollTop = (elem.scrollHeight - elem.clientHeight) * (vertical / 100);
+        Buffer.scrollTo(elem,
+                        horizontal == null ? null
+                                           : (elem.scrollWidth - elem.clientWidth) * (horizontal / 100),
+                        vertical   == null ? null
+                                           : (elem.scrollHeight - elem.clientHeight) * (vertical / 100));
     },
 
     openUploadPrompt: function openUploadPrompt(elem) {
diff --git a/common/modules/base.jsm b/common/modules/base.jsm
index bbae6553..daee9992 100644
--- a/common/modules/base.jsm
+++ b/common/modules/base.jsm
@@ -690,10 +690,11 @@ function update(target) {
                 desc = desc.value.init(k) || desc.value;
             if (typeof desc.value == "function" && Object.getPrototypeOf(target)) {
                 let func = desc.value;
-                desc.value.superapply = function (self, args)
+                desc.value.__defineGetter__("super", function () Object.getPrototypeOf(target)[k]);
+                desc.value.superapply = function superapply(self, args)
                     let (meth = Object.getPrototypeOf(target)[k])
                         meth && meth.apply(self, args);
-                desc.value.supercall = function (self)
+                desc.value.supercall = function supercall(self)
                     func.superapply(self, Array.slice(arguments, 1));
             }
             Object.defineProperty(target, k, desc);
diff --git a/common/modules/util.jsm b/common/modules/util.jsm
index 50ed3c9a..4c769000 100644
--- a/common/modules/util.jsm
+++ b/common/modules/util.jsm
@@ -988,6 +988,27 @@ var Util = Module("Util", XPCOM([Ci.nsIObserver, Ci.nsISupportsWeakReference]),
                 }), true);
     },
 
+    overlayObject: function (object, overrides) {
+        let original = Object.create(object);
+        overrides = update(Object.create(original), overrides);
+
+        for each (let k in Object.getOwnPropertyNames(overrides)) {
+            let orig, desc = Object.getOwnPropertyDescriptor(overrides, k);
+            if (desc.value instanceof Class.Property)
+                desc = desc.value.init(k) || desc.value;
+
+            for (let obj = object; obj && !orig; obj = Object.getPrototypeOf(obj))
+                if (orig = Object.getOwnPropertyDescriptor(obj, k))
+                    Object.defineProperty(original, k, orig);
+
+            Object.defineProperty(object, k, desc);
+        }
+        return function unwrap() {
+            for each (let k in Object.getOwnPropertyNames(original))
+                Object.defineProperty(object, k, Object.getOwnPropertyDescriptor(original, k));
+        }
+    },
+
     overlayWindow: function (url, fn) {
         if (url instanceof Ci.nsIDOMWindow)
             util._loadOverlay(url, fn);