--- a/browser/metro/base/content/helperui/MenuUI.js
+++ b/browser/metro/base/content/helperui/MenuUI.js
@@ -383,16 +383,18 @@ MenuPopup.prototype = {
     window.removeEventListener("mousedown", this, true);
     Elements.stack.removeEventListener("PopupChanged", this, false);
 
     let self = this;
     this._panel.addEventListener("transitionend", function () {
       self._panel.removeEventListener("transitionend", arguments.callee);
       self._panel.removeAttribute("hiding");
       self._panel.hidden = true;
+      self._popup.style.maxWidth = "none";
+      self._popup.style.maxHeight = "none";
 
       let event = document.createEvent("Events");
       event.initEvent("popuphidden", true, false);
       document.dispatchEvent(event);
     });
 
     this._panel.setAttribute("hiding", "true");
     setTimeout(()=>this._panel.removeAttribute("showing"), 0);
@@ -427,39 +429,47 @@ MenuPopup.prototype = {
       aX -= width;
 
     if (aPositionOptions.bottomAligned)
       aY -= height;
 
     if (aPositionOptions.centerHorizontally)
       aX -= halfWidth;
 
-    if (aX < 0) {
-      aX = 0;
+    // Always leave some padding.
+    if (aX < kPositionPadding) {
+      aX = kPositionPadding;
     } else if (aX + width + kPositionPadding > screenWidth){
-      aX = screenWidth - width - kPositionPadding;
+      // Don't let the popup overflow to the right.
+      aX = Math.max(screenWidth - width - kPositionPadding, kPositionPadding);
     }
 
-    if (aY < 0 && aPositionOptions.moveBelowToFit) {
+    if (aY < kPositionPadding  && aPositionOptions.moveBelowToFit) {
       // show context menu below when it doesn't fit.
       aY = aPositionOptions.yPos;
-    } else if (aY < 0) {
-      aY = 0;
+    }
+
+    if (aY < kPositionPadding) {
+      aY = kPositionPadding;
+    } else if (aY + height + kPositionPadding > screenHeight){
+      aY = Math.max(screenHeight - height - kPositionPadding, kPositionPadding);
     }
 
     this._panel.left = aX;
     this._panel.top = aY;
 
-    if (!aPositionOptions.maxWidth) {
-      let excessY = (aY + height + kPositionPadding - screenHeight);
-      this._popup.style.maxHeight = (excessY > 0) ? (height - excessY) + "px" : "none";
+    if (!aPositionOptions.maxHeight) {
+      // Make sure it fits in the window.
+      let popupHeight = Math.min(aY + height + kPositionPadding, screenHeight - aY - kPositionPadding);
+      this._popup.style.maxHeight = popupHeight + "px";
     }
-    if (!aPositionOptions.maxHeight) {
-      let excessX = (aX + width + kPositionPadding - screenWidth);
-      this._popup.style.maxWidth = (excessX > 0) ? (width - excessX) + "px" : "none";
+
+    if (!aPositionOptions.maxWidth) {
+      let popupWidth = Math.min(aX + width + kPositionPadding, screenWidth - aX - kPositionPadding);
+      this._popup.style.maxWidth = popupWidth + "px";
     }
   },
 
   handleEvent: function handleEvent(aEvent) {
     switch (aEvent.type) {
       case "keypress":
         if (!this._wantTypeBehind) {
           // Hide the context menu so you can't type behind it.