diff --git a/app/assets/javascripts/discourse/lib/Markdown.Editor.js b/app/assets/javascripts/discourse/lib/Markdown.Editor.js
index 1880beec587..8a267d2f34d 100644
--- a/app/assets/javascripts/discourse/lib/Markdown.Editor.js
+++ b/app/assets/javascripts/discourse/lib/Markdown.Editor.js
@@ -40,6 +40,11 @@
         nav = window.navigator,
         SETTINGS = { lineLength: 72 },
 
+    // Used to work around some browser bugs where we can't use feature testing.
+        uaSniffed = {
+            isIE: /msie/.test(nav.userAgent.toLowerCase()),
+            isIE_5or6: /msie 6/.test(nav.userAgent.toLowerCase()) || /msie 5/.test(nav.userAgent.toLowerCase())
+        };
 
     var defaultsStrings = {
         bold: "Strong <strong> Ctrl+B",
@@ -330,21 +335,43 @@
     // Returns true if the DOM element is visible, false if it's hidden.
     // Checks if display is anything other than none.
     util.isVisible = function (elem) {
-        return window.getComputedStyle(elem, null).getPropertyValue("display") !== "none";
+
+        if (window.getComputedStyle) {
+            // Most browsers
+            return window.getComputedStyle(elem, null).getPropertyValue("display") !== "none";
+        }
+        else if (elem.currentStyle) {
+            // IE
+            return elem.currentStyle["display"] !== "none";
+        }
     };
 
 
     // Adds a listener callback to a DOM element which is fired on a specified
     // event.
     util.addEvent = function (elem, event, listener) {
-        elem.addEventListener(event, listener, false);
+        if (elem.attachEvent) {
+            // IE only.  The "on" is mandatory.
+            elem.attachEvent("on" + event, listener);
+        }
+        else {
+            // Other browsers.
+            elem.addEventListener(event, listener, false);
+        }
     };
 
 
     // Removes a listener callback from a DOM element which is fired on a specified
     // event.
     util.removeEvent = function (elem, event, listener) {
-        elem.removeEventListener(event, listener, false);
+        if (elem.detachEvent) {
+            // IE only.  The "on" is mandatory.
+            elem.detachEvent("on" + event, listener);
+        }
+        else {
+            // Other browsers.
+            elem.removeEventListener(event, listener, false);
+        }
     };
 
     // Converts \r\n and \r to \n.
@@ -427,8 +454,21 @@
             scrollHeight = doc.body.offsetHeight;
         }
 
-        innerWidth = self.innerWidth;
-        innerHeight = self.innerHeight;
+        if (self.innerHeight) {
+            // Non-IE browser
+            innerWidth = self.innerWidth;
+            innerHeight = self.innerHeight;
+        }
+        else if (doc.documentElement && doc.documentElement.clientHeight) {
+            // Some versions of IE (IE 6 w/ a DOCTYPE declaration)
+            innerWidth = doc.documentElement.clientWidth;
+            innerHeight = doc.documentElement.clientHeight;
+        }
+        else if (doc.body) {
+            // Other versions of IE
+            innerWidth = doc.body.clientWidth;
+            innerHeight = doc.body.clientHeight;
+        }
 
         var maxWidth = Math.max(scrollWidth, innerWidth);
         var maxHeight = Math.max(scrollHeight, innerHeight);
@@ -456,7 +496,7 @@
                 }
             }
 
-            if (mode != "moving") {
+            if (!uaSniffed.isIE || mode != "moving") {
                 timer = setTimeout(refreshState, 1);
             }
             else {
@@ -559,7 +599,9 @@
 
             if ((event.ctrlKey || event.metaKey) && !event.altKey) {
 
-                var keyCodeChar = String.fromCharCode(event.charCode);
+                // IE and Opera do not support charCode.
+                var keyCode = event.charCode || event.keyCode;
+                var keyCodeChar = String.fromCharCode(keyCode);
 
                 switch (keyCodeChar.toLowerCase()) {
 
@@ -639,7 +681,7 @@
             });
 
             var handlePaste = function () {
-                if (inputStateObj && inputStateObj.text != panels.input.value) {
+                if (uaSniffed.isIE || (inputStateObj && inputStateObj.text != panels.input.value)) {
                     if (timer == undefined) {
                         mode = "paste";
                         saveState();
@@ -1001,6 +1043,24 @@
 
         var isFirstTimeFilled = true;
 
+        // IE doesn't let you use innerHTML if the element is contained somewhere in a table
+        // (which is the case for inline editing) -- in that case, detach the element, set the
+        // value, and reattach. Yes, that *is* ridiculous.
+        var ieSafePreviewSet = function (previewText) {
+            var ieSafeSet = function(panel, text) {
+              var parent = panel.parentNode;
+              var sibling = panel.nextSibling;
+              parent.removeChild(panel);
+              panel.innerHTML = text;
+              if (!sibling)
+                parent.appendChild(panel);
+              else
+                parent.insertBefore(panel, sibling);
+            };
+
+            ieSafeSet(panels.preview, previewText);
+        }
+
         var nonSuckyBrowserPreviewSet = function (previewText) {
             panels.preview.innerHTML = previewText;
         }
@@ -1012,8 +1072,13 @@
             if (previewSetter)
                 return previewSetter(previewText);
 
-            nonSuckyBrowserPreviewSet(previewText);
-            previewSetter = nonSuckyBrowserPreviewSet;
+            try {
+                nonSuckyBrowserPreviewSet(previewText);
+                previewSetter = nonSuckyBrowserPreviewSet;
+            } catch (e) {
+                previewSetter = ieSafePreviewSet;
+                previewSetter(previewText);
+            }
         };
 
         var pushPreviewHtml = function (previewText) {
@@ -1032,7 +1097,14 @@
 
             var fullTop = position.getTop(panels.input) - getDocScrollTop();
 
-            window.scrollBy(0, fullTop - emptyTop);
+            if (uaSniffed.isIE) {
+                setTimeout(function () {
+                    window.scrollBy(0, fullTop - emptyTop);
+                }, 0);
+            }
+            else {
+                window.scrollBy(0, fullTop - emptyTop);
+            }
         };
 
         var init = function () {
@@ -1063,12 +1135,24 @@
 
         style.zIndex = "2000";
 
-        style.opacity = "0.5";
+        if (uaSniffed.isIE) {
+            style.filter = "alpha(opacity=50)";
+        }
+        else {
+            style.opacity = "0.5";
+        }
 
         var pageSize = position.getPageSize();
         style.height = pageSize[1] + "px";
-        style.left = "0";
-        style.width = "100%";
+
+        if (uaSniffed.isIE) {
+            style.left = doc.documentElement.scrollLeft;
+            style.width = doc.documentElement.clientWidth;
+        }
+        else {
+            style.left = "0";
+            style.width = "100%";
+        }
 
         doc.body.appendChild(background);
         return background;
@@ -1195,6 +1279,11 @@
             dialog.style.top = "50%";
             dialog.style.left = "50%";
             dialog.style.display = "block";
+            if (uaSniffed.isIE_5or6) {
+                dialog.style.position = "absolute";
+                dialog.style.top = doc.documentElement.scrollTop + 200 + "px";
+                dialog.style.left = "50%";
+            }
             doc.body.appendChild(dialog);
 
             // This has to be done AFTER adding the dialog to the form if you
@@ -1299,6 +1388,16 @@
             }
         });
 
+        // special handler because IE clears the context of the textbox on ESC
+        if (uaSniffed.isIE) {
+            util.addEvent(inputBox, "keydown", function (key) {
+                var code = key.keyCode;
+                if (code === 27) {
+                    return false;
+                }
+            });
+        }
+
 
         // Perform the button's action.
         function doClick(button) {
@@ -1366,6 +1465,19 @@
             if (isEnabled) {
                 button.disabled = false
 
+                // IE tries to select the background image "button" text (it's
+                // implemented in a list item) so we have to cache the selection
+                // on mousedown.
+                if (uaSniffed.isIE) {
+                    button.onmousedown = function () {
+                        if (doc.activeElement && doc.activeElement !== panels.input) { // we're not even in the input box, so there's no selection
+                            return;
+                        }
+                        panels.ieCachedRange = document.selection.createRange();
+                        panels.ieCachedScrollTop = panels.input.scrollTop;
+                    };
+                }
+
                 if (!button.isHelp) {
                     button.onclick = function () {
                         if (this.onmouseout) {