diff --git a/layout/xul/base/public/nsIPopupBoxObject.idl b/layout/xul/base/public/nsIPopupBoxObject.idl
index 6bff30c8a82a..f4548629963c 100644
--- a/layout/xul/base/public/nsIPopupBoxObject.idl
+++ b/layout/xul/base/public/nsIPopupBoxObject.idl
@@ -10,7 +10,7 @@ interface nsIDOMNode;
 interface nsIDOMEvent;
 interface nsIDOMClientRect;
 
-[scriptable, uuid(DF60BA02-005B-4F61-AB1C-5632D0779DB4)]
+[scriptable, uuid(ACCEA57B-C3D8-4B6E-9101-90F04EE9DEA0)]
 interface nsIPopupBoxObject : nsISupports
 {
   /**
@@ -166,11 +166,6 @@ interface nsIPopupBoxObject : nsISupports
                     in AString position,
                     in long x, in long y,
                     in boolean attributesOverride);
-
-  /** Returns the alignment position where the popup has appeared relative to its
-   *  anchor node or point, accounting for any flipping that occurred.
-   */
-  readonly attribute AString alignmentPosition;
 };
 
 %{C++
diff --git a/layout/xul/base/src/nsMenuPopupFrame.cpp b/layout/xul/base/src/nsMenuPopupFrame.cpp
index 36ad276839fd..9d6c7259cfcb 100644
--- a/layout/xul/base/src/nsMenuPopupFrame.cpp
+++ b/layout/xul/base/src/nsMenuPopupFrame.cpp
@@ -82,7 +82,6 @@ nsMenuPopupFrame::nsMenuPopupFrame(nsIPresShell* aShell, nsStyleContext* aContex
   mPopupState(ePopupClosed),
   mPopupAlignment(POPUPALIGNMENT_NONE),
   mPopupAnchor(POPUPALIGNMENT_NONE),
-  mPosition(POPUPPOSITION_UNKNOWN),
   mConsumeRollupEvent(nsIPopupBoxObject::ROLLUP_DEFAULT),
   mFlipBoth(false),
   mIsOpenChanged(false),
@@ -535,8 +534,6 @@ nsMenuPopupFrame::InitPositionFromAnchorAlign(const nsAString& aAnchor,
     mPopupAlignment = POPUPALIGNMENT_BOTTOMRIGHT;
   else
     mPopupAlignment = POPUPALIGNMENT_NONE;
-
-  mPosition = POPUPPOSITION_UNKNOWN;
 }
 
 void
@@ -554,7 +551,6 @@ nsMenuPopupFrame::InitializePopup(nsIContent* aAnchorContent,
   mXPos = aXPos;
   mYPos = aYPos;
   mAdjustOffsetForContextMenu = false;
-  mPosition = POPUPPOSITION_UNKNOWN;
 
   // if aAttributesOverride is true, then the popupanchor, popupalign and
   // position attributes on the <popup> override those values passed in.
@@ -590,52 +586,42 @@ nsMenuPopupFrame::InitializePopup(nsIContent* aAnchorContent,
     else if (position.EqualsLiteral("before_start")) {
       mPopupAnchor = POPUPALIGNMENT_TOPLEFT;
       mPopupAlignment = POPUPALIGNMENT_BOTTOMLEFT;
-      mPosition = POPUPPOSITION_BEFORESTART;
     }
     else if (position.EqualsLiteral("before_end")) {
       mPopupAnchor = POPUPALIGNMENT_TOPRIGHT;
       mPopupAlignment = POPUPALIGNMENT_BOTTOMRIGHT;
-      mPosition = POPUPPOSITION_BEFOREEND;
     }
     else if (position.EqualsLiteral("after_start")) {
       mPopupAnchor = POPUPALIGNMENT_BOTTOMLEFT;
       mPopupAlignment = POPUPALIGNMENT_TOPLEFT;
-      mPosition = POPUPPOSITION_AFTERSTART;
     }
     else if (position.EqualsLiteral("after_end")) {
       mPopupAnchor = POPUPALIGNMENT_BOTTOMRIGHT;
       mPopupAlignment = POPUPALIGNMENT_TOPRIGHT;
-      mPosition = POPUPPOSITION_AFTEREND;
     }
     else if (position.EqualsLiteral("start_before")) {
       mPopupAnchor = POPUPALIGNMENT_TOPLEFT;
       mPopupAlignment = POPUPALIGNMENT_TOPRIGHT;
-      mPosition = POPUPPOSITION_STARTBEFORE;
     }
     else if (position.EqualsLiteral("start_after")) {
       mPopupAnchor = POPUPALIGNMENT_BOTTOMLEFT;
       mPopupAlignment = POPUPALIGNMENT_BOTTOMRIGHT;
-      mPosition = POPUPPOSITION_STARTAFTER;
     }
     else if (position.EqualsLiteral("end_before")) {
       mPopupAnchor = POPUPALIGNMENT_TOPRIGHT;
       mPopupAlignment = POPUPALIGNMENT_TOPLEFT;
-      mPosition = POPUPPOSITION_ENDBEFORE;
     }
     else if (position.EqualsLiteral("end_after")) {
       mPopupAnchor = POPUPALIGNMENT_BOTTOMRIGHT;
       mPopupAlignment = POPUPALIGNMENT_BOTTOMLEFT;
-      mPosition = POPUPPOSITION_ENDAFTER;
     }
     else if (position.EqualsLiteral("overlap")) {
       mPopupAnchor = POPUPALIGNMENT_TOPLEFT;
       mPopupAlignment = POPUPALIGNMENT_TOPLEFT;
-      mPosition = POPUPPOSITION_OVERLAP;
     }
     else if (position.EqualsLiteral("after_pointer")) {
       mPopupAnchor = POPUPALIGNMENT_TOPLEFT;
       mPopupAlignment = POPUPALIGNMENT_TOPLEFT;
-      mPosition = POPUPPOSITION_AFTERPOINTER;
       // XXXndeakin this is supposed to anchor vertically after, but with the
       // horizontal position as the mouse pointer.
       mYPos += 21;
@@ -1922,51 +1908,6 @@ nsMenuPopupFrame::SetConsumeRollupEvent(uint32_t aConsumeMode)
   mConsumeRollupEvent = aConsumeMode;
 }
 
-int8_t
-nsMenuPopupFrame::GetAlignmentPosition() const
-{
-  // The code below handles most cases of alignment, anchor and position values. Those that are
-  // not handled just return POPUPPOSITION_UNKNOWN.
-
-  if (mPosition == POPUPPOSITION_OVERLAP || mPosition == POPUPPOSITION_AFTERPOINTER)
-    return mPosition;
-
-  int8_t position = mPosition;
-
-  if (position == POPUPPOSITION_UNKNOWN) {
-    switch (mPopupAnchor) {
-      case POPUPALIGNMENT_BOTTOMCENTER:
-        position = mPopupAlignment == POPUPALIGNMENT_TOPRIGHT ?
-                     POPUPPOSITION_AFTEREND : POPUPPOSITION_AFTERSTART;
-        break;
-      case POPUPALIGNMENT_TOPCENTER:
-        position = mPopupAlignment == POPUPALIGNMENT_BOTTOMRIGHT ?
-                     POPUPPOSITION_BEFOREEND : POPUPPOSITION_BEFORESTART;
-        break;
-      case POPUPALIGNMENT_LEFTCENTER:
-        position = mPopupAlignment == POPUPALIGNMENT_BOTTOMRIGHT ?
-                     POPUPPOSITION_STARTAFTER : POPUPPOSITION_STARTBEFORE;
-        break;
-      case POPUPALIGNMENT_RIGHTCENTER:
-        position = mPopupAlignment == POPUPALIGNMENT_BOTTOMLEFT ?
-                     POPUPPOSITION_ENDAFTER : POPUPPOSITION_ENDBEFORE;
-        break;
-      default:
-        break;
-    }
-  }
-
-  if (mHFlip) {
-    position = POPUPPOSITION_HFLIP(position);
-  }
-
-  if (mVFlip) {
-    position = POPUPPOSITION_VFLIP(position);
-  }
-
-  return position;
-}
-
 /**
  * KEEP THIS IN SYNC WITH nsContainerFrame::CreateViewForFrame
  * as much as possible. Until we get rid of views finally...
diff --git a/layout/xul/base/src/nsMenuPopupFrame.h b/layout/xul/base/src/nsMenuPopupFrame.h
index c96575026440..c7aa8c9c2cc7 100644
--- a/layout/xul/base/src/nsMenuPopupFrame.h
+++ b/layout/xul/base/src/nsMenuPopupFrame.h
@@ -79,23 +79,6 @@ enum FlipStyle {
 #define POPUPALIGNMENT_TOPCENTER 17
 #define POPUPALIGNMENT_BOTTOMCENTER 18
 
-// The constants here are selected so that horizontally and vertically flipping
-// can be easily handled using the two flip macros below.
-#define POPUPPOSITION_UNKNOWN -1
-#define POPUPPOSITION_BEFORESTART 0
-#define POPUPPOSITION_BEFOREEND 1
-#define POPUPPOSITION_AFTERSTART 2
-#define POPUPPOSITION_AFTEREND 3
-#define POPUPPOSITION_STARTBEFORE 4
-#define POPUPPOSITION_ENDBEFORE 5
-#define POPUPPOSITION_STARTAFTER 6
-#define POPUPPOSITION_ENDAFTER 7
-#define POPUPPOSITION_OVERLAP 8
-#define POPUPPOSITION_AFTERPOINTER 9
-
-#define POPUPPOSITION_HFLIP(v) (v ^ 1)
-#define POPUPPOSITION_VFLIP(v) (v ^ 2)
-
 #define INC_TYP_INTERVAL  1000  // 1s. If the interval between two keypresses is shorter than this, 
                                 //   treat as a continue typing
 // XXX, kyle.yuan@sun.com, there are 4 definitions for the same purpose:
@@ -332,9 +315,6 @@ public:
 
   nsIntPoint GetLastClientOffset() const { return mLastClientOffset; }
 
-  // Return the alignment of the popup
-  int8_t GetAlignmentPosition() const;
-
 protected:
 
   // returns the popup's level.
@@ -430,8 +410,6 @@ protected:
   // popup alignment relative to the anchor node
   int8_t mPopupAlignment;
   int8_t mPopupAnchor;
-  int8_t mPosition;
-
   // One of nsIPopupBoxObject::ROLLUP_DEFAULT/ROLLUP_CONSUME/ROLLUP_NO_CONSUME
   int8_t mConsumeRollupEvent;
   bool mFlipBoth; // flip in both directions
diff --git a/layout/xul/base/src/nsPopupBoxObject.cpp b/layout/xul/base/src/nsPopupBoxObject.cpp
index 0962c81cd68e..4266ba1d7858 100644
--- a/layout/xul/base/src/nsPopupBoxObject.cpp
+++ b/layout/xul/base/src/nsPopupBoxObject.cpp
@@ -307,56 +307,6 @@ nsPopupBoxObject::GetOuterScreenRect(nsIDOMClientRect** aRect)
   return NS_OK;
 }
 
-NS_IMETHODIMP
-nsPopupBoxObject::GetAlignmentPosition(nsAString& positionStr)
-{
-  positionStr.Truncate();
-
-  // This needs to flush layout.
-  nsMenuPopupFrame *menuPopupFrame = do_QueryFrame(GetFrame(true));
-  if (!menuPopupFrame)
-    return NS_OK;
-
-  int8_t position = menuPopupFrame->GetAlignmentPosition();
-  switch (position) {
-    case POPUPPOSITION_AFTERSTART:
-      positionStr.AssignLiteral("after_start");
-      break;
-    case POPUPPOSITION_AFTEREND:
-      positionStr.AssignLiteral("after_end");
-      break;
-    case POPUPPOSITION_BEFORESTART:
-      positionStr.AssignLiteral("before_start");
-      break;
-    case POPUPPOSITION_BEFOREEND:
-      positionStr.AssignLiteral("before_end");
-      break;
-    case POPUPPOSITION_STARTBEFORE:
-      positionStr.AssignLiteral("start_before");
-      break;
-    case POPUPPOSITION_ENDBEFORE:
-      positionStr.AssignLiteral("end_before");
-      break;
-    case POPUPPOSITION_STARTAFTER:
-      positionStr.AssignLiteral("start_after");
-      break;
-    case POPUPPOSITION_ENDAFTER:
-      positionStr.AssignLiteral("end_after");
-      break;
-    case POPUPPOSITION_OVERLAP:
-      positionStr.AssignLiteral("overlap");
-      break;
-    case POPUPPOSITION_AFTERPOINTER:
-      positionStr.AssignLiteral("after_pointer");
-      break;
-    default:
-      // Leave as an empty string.
-      break;
-  }
-
-  return NS_OK;
-}
-
 // Creation Routine ///////////////////////////////////////////////////////////////////////
 
 nsresult
diff --git a/toolkit/content/tests/chrome/test_arrowpanel.xul b/toolkit/content/tests/chrome/test_arrowpanel.xul
index 53b35ce4367b..43480bef3c43 100644
--- a/toolkit/content/tests/chrome/test_arrowpanel.xul
+++ b/toolkit/content/tests/chrome/test_arrowpanel.xul
@@ -25,7 +25,7 @@
   <label id="panellabel" value="This is some text." height="65"/>
 </panel>
 
-<panel id="bigpanel" type="arrow" onpopupshown="checkBigPanel(this)" onpopuphidden="runNextTest.next()">
+<panel id="bigpanel" type="arrow" onpopupshown="checkBigPanel(this)" onpopuphidden="SimpleTest.finish()">
   <button label="This is some text." height="3000"/>
 </panel>
 
@@ -35,7 +35,7 @@
 SimpleTest.waitForExplicitFinish();
 
 var expectedAnchor = null;
-var expectedSide = "", expectedAnchorEdge = "", expectedPack = "", expectedAlignment = "";
+var expectedSide = "", expectedAnchorEdge = "", expectedPack = "";
 var zoomFactor = 1;
 var runNextTest;
 
@@ -49,122 +49,108 @@ function nextTest()
 {
   var panel = $("panel");
 
-  function openPopup(position, anchor, expected, anchorEdge, pack, alignment)
+  function openPopup(position, anchor, expected, anchorEdge, pack)
   {
     expectedAnchor = anchor instanceof Node ? anchor : $(anchor);
     expectedSide = expected;
     expectedAnchorEdge = anchorEdge;
     expectedPack = pack;
-    expectedAlignment = alignment == undefined ? position : alignment;
 
     panel.removeAttribute("side");
     panel.openPopup(expectedAnchor, position, 0, 0, false, false, null);
   }
 
-  for (var iter = 0; iter < 2; iter++) {
-    openPopup("after_start", "topleft", "top", "left", "start");
-    yield;
-    openPopup("after_start", "bottomleft", "bottom", "left", "start", "before_start");
-    yield;
-    openPopup("before_start", "topleft", "top", "left", "start", "after_start");
-    yield;
-    openPopup("before_start", "bottomleft", "bottom", "left", "start");
-    yield;
-    openPopup("after_start", "middle", "top", "left", "start");
-    yield;
-    openPopup("before_start", "middle", "bottom", "left", "start");
-    yield;
+  openPopup("after_start", "topleft", "top", "left", "start");
+  yield;
+  openPopup("after_start", "bottomleft", "bottom", "left", "start");
+  yield;
+  openPopup("before_start", "topleft", "top", "left", "start");
+  yield;
+  openPopup("before_start", "bottomleft", "bottom", "left", "start");
+  yield;
+  openPopup("after_start", "middle", "top", "left", "start");
+  yield;
+  openPopup("before_start", "middle", "bottom", "left", "start");
+  yield;
 
-    openPopup("after_start", "topright", "top", "right", "end", "after_end");
-    yield;
-    openPopup("after_start", "bottomright", "bottom", "right", "end", "before_end");
-    yield;
-    openPopup("before_start", "topright", "top", "right", "end", "after_end");
-    yield;
-    openPopup("before_start", "bottomright", "bottom", "right", "end", "before_end");
-    yield;
+  openPopup("after_start", "topright", "top", "right", "end");
+  yield;
+  openPopup("after_start", "bottomright", "bottom", "right", "end");
+  yield;
+  openPopup("before_start", "topright", "top", "right", "end");
+  yield;
+  openPopup("before_start", "bottomright", "bottom", "right", "end");
+  yield;
 
-    openPopup("after_end", "middle", "top", "right", "end");
-    yield;
-    openPopup("before_end", "middle", "bottom", "right", "end");
-    yield;
+  openPopup("after_end", "middle", "top", "right", "end");
+  yield;
+  openPopup("before_end", "middle", "bottom", "right", "end");
+  yield;
 
-    openPopup("start_before", "topleft", "left", "top", "start", "end_before");
-    yield;
-    openPopup("start_before", "topright", "right", "top", "start");
-    yield;
-    openPopup("end_before", "topleft", "left", "top", "start");
-    yield;
-    openPopup("end_before", "topright", "right", "top", "start", "start_before");
-    yield;
-    openPopup("start_before", "middle", "right", "top", "start");
-    yield;
-    openPopup("end_before", "middle", "left", "top", "start");
-    yield;
+  openPopup("start_before", "topleft", "left", "top", "start");
+  yield;
+  openPopup("start_before", "topright", "right", "top", "start");
+  yield;
+  openPopup("end_before", "topleft", "left", "top", "start");
+  yield;
+  openPopup("end_before", "topright", "right", "top", "start");
+  yield;
+  openPopup("start_before", "middle", "right", "top", "start");
+  yield;
+  openPopup("end_before", "middle", "left", "top", "start");
+  yield;
 
-    openPopup("start_before", "bottomleft", "left", "bottom", "end", "end_after");
-    yield;
-    openPopup("start_before", "bottomright", "right", "bottom", "end", "start_after");
-    yield;
-    openPopup("end_before", "bottomleft", "left", "bottom", "end", "end_after");
-    yield;
-    openPopup("end_before", "bottomright", "right", "bottom", "end", "start_after");
-    yield;
+  openPopup("start_before", "bottomleft", "left", "bottom", "end");
+  yield;
+  openPopup("start_before", "bottomright", "right", "bottom", "end");
+  yield;
+  openPopup("end_before", "bottomleft", "left", "bottom", "end");
+  yield;
+  openPopup("end_before", "bottomright", "right", "bottom", "end");
+  yield;
 
-    openPopup("start_after", "middle", "right", "bottom", "end");
-    yield;
-    openPopup("end_after", "middle", "left", "bottom", "end");
-    yield;
+  openPopup("start_after", "middle", "right", "bottom", "end");
+  yield;
+  openPopup("end_after", "middle", "left", "bottom", "end");
+  yield;
 
-    openPopup("topcenter bottomleft", "bottomleft", "bottom", "center left", "start", "before_start");
-    yield;
-    openPopup("bottomcenter topleft", "topleft", "top", "center left", "start", "after_start");
-    yield;
-    openPopup("topcenter bottomright", "bottomright", "bottom", "center right", "end", "before_end");
-    yield;
-    openPopup("bottomcenter topright", "topright", "top", "center right", "end", "after_end");
-    yield;
-    openPopup("topcenter bottomleft", "middle", "bottom", "center left", "start", "before_start");
-    yield;
-    openPopup("bottomcenter topleft", "middle", "top", "center left", "start", "after_start");
-    yield;
+  openPopup("topcenter bottomleft", "bottomleft", "bottom", "center left", "start");
+  yield;
+  openPopup("bottomcenter topleft", "topleft", "top", "center left", "start");
+  yield;
+  openPopup("topcenter bottomright", "bottomright", "bottom", "center right", "end");
+  yield;
+  openPopup("bottomcenter topright", "topright", "top", "center right", "end");
+  yield;
+  openPopup("topcenter bottomleft", "middle", "bottom", "center left", "start");
+  yield;
+  openPopup("bottomcenter topleft", "middle", "top", "center left", "start");
+  yield;
 
-    openPopup("leftcenter topright", "middle", "right", "center top", "start", "start_before");
-    yield;
-    openPopup("rightcenter bottomleft", "middle", "left", "center bottom", "end", "end_after");
-    yield;
+  openPopup("leftcenter topright", "middle", "right", "center top", "start");
+  yield;
+  openPopup("rightcenter bottomleft", "middle", "left", "center bottom", "end");
+  yield;
 
 /*
-    XXXndeakin disable these parts of the test which often cause problems, see bug 626563
+  XXXndeakin disable these parts of the test which often cause problems, see bug 626563
 
-    openPopup("after_start", frames[0].document.getElementById("input"), "top", "left", "start");
-    yield;
+  openPopup("after_start", frames[0].document.getElementById("input"), "top", "left", "start");
+  yield;
 
-    setScale(frames[0], 1.5);
-    openPopup("after_start", frames[0].document.getElementById("input"), "top", "left", "start");
-    yield;
+  setScale(frames[0], 1.5);
+  openPopup("after_start", frames[0].document.getElementById("input"), "top", "left", "start");
+  yield;
 
-    setScale(frames[0], 2.5);
-    openPopup("before_start", frames[0].document.getElementById("input"), "bottom", "left", "start");
-    yield;
+  setScale(frames[0], 2.5);
+  openPopup("before_start", frames[0].document.getElementById("input"), "bottom", "left", "start");
+  yield;
 
-    setScale(frames[0], 1);
+  setScale(frames[0], 1);
 */
 
-    $("bigpanel").openPopup($("topleft"), "after_start", 0, 0, false, false, null, "start");
-    yield;
-
-    // switch to rtl mode
-    document.documentElement.style.direction = "rtl";
-    $("topleft").setAttribute("right", "15");
-    $("topright").setAttribute("left", "15");
-    $("bottomleft").setAttribute("right", "15");
-    $("bottomright").setAttribute("left", "15");
-    $("topleft").removeAttribute("left");
-    $("topright").removeAttribute("right");
-    $("bottomleft").removeAttribute("left");
-    $("bottomright").removeAttribute("right");
-  }
+  $("bigpanel").openPopup($("topleft"), "after_start", 0, 0, false, false, null, "start");
+  yield;
 
   SimpleTest.finish();
   yield;
@@ -190,15 +176,6 @@ function checkPanelPosition(panel)
     vwinpos = framerect.top;
   }
 
-  // Positions are reversed in rtl yet the coordinates used in the computations
-  // are not, so flip the expected label side and anchor edge.
-  var isRTL = (window.getComputedStyle(panel).direction == "rtl");
-  if (isRTL) {
-    var flipLeftRight = function (val) val == "left" ? "right" : "left";
-    expectedAnchorEdge = expectedAnchorEdge.replace(/(left|right)/, flipLeftRight);
-    expectedSide = expectedSide.replace(/(left|right)/, flipLeftRight);
-  }
-
   var panelRect = panel.getBoundingClientRect();
   var anchorRect = anchor.getBoundingClientRect();
   var labelBO = $("panellabel").boxObject;
@@ -260,7 +237,6 @@ function checkPanelPosition(panel)
   is(arrow.getAttribute("side"), expectedSide, "panel arrow side");
   is(arrow.hidden, false, "panel hidden");
   is(arrow.parentNode.pack, expectedPack, "panel arrow pack");
-  is(panel.alignmentPosition, expectedAlignment, "panel alignmentPosition");
 
   panel.hidePopup();
 }
diff --git a/toolkit/content/widgets/popup.xml b/toolkit/content/widgets/popup.xml
index a82501b9c695..9e2911b43e9e 100644
--- a/toolkit/content/widgets/popup.xml
+++ b/toolkit/content/widgets/popup.xml
@@ -126,14 +126,6 @@
         ]]>
         </setter>
       </property>
-
-      <property name="alignmentPosition" readonly="true">
-        <getter>
-        <![CDATA[
-          return this.popupBoxObject.alignmentPosition;
-        ]]>
-        </getter>
-      </property>
       
       <method name="enableKeyboardNavigator">
         <parameter name="aEnableKeyboardNavigator"/>
@@ -330,7 +322,7 @@
       <xul:box anonid="container" class="panel-arrowcontainer" flex="1"
                xbl:inherits="side,panelopen">
         <xul:box anonid="arrowbox" class="panel-arrowbox">
-          <xul:image anonid="arrow" class="panel-arrow" xbl:inherits="side"/>
+          <xul:image anonid="arrow" class="panel-arrow"/>
         </xul:box>
         <xul:box class="panel-arrowcontent" xbl:inherits="side,align,dir,orient,pack" flex="1">
           <children/>
@@ -344,6 +336,8 @@
     <handlers>
       <handler event="popupshowing" phase="target">
       <![CDATA[
+        var container = document.getAnonymousElementByAttribute(this, "anonid", "container");
+        var arrowbox = document.getAnonymousElementByAttribute(this, "anonid", "arrowbox");
         var arrow = document.getAnonymousElementByAttribute(this, "anonid", "arrow");
 
         var anchor = this.anchorNode;
@@ -352,43 +346,118 @@
           return;
         }
 
-        var container = document.getAnonymousElementByAttribute(this, "anonid", "container");
-        var arrowbox = document.getAnonymousElementByAttribute(this, "anonid", "arrowbox");
-
-        var position = this.alignmentPosition;
-        if (position.indexOf("start_") == 0 || position.indexOf("end_") == 0) {
-          container.orient = "";
-          arrowbox.orient = "vertical";
-          arrowbox.pack = (position.indexOf("_after") > 0) ? "end" : "start";
-
-          // The assigned side stays the same regardless of direction.
-          var isRTL = (window.getComputedStyle(this).direction == "rtl");
-
-          if (position.indexOf("start_") == 0) {
-            container.dir = "reverse";
-            this.setAttribute("side", isRTL ? "left" : "right");
-          }
-          else {
-            container.dir = "";
-            this.setAttribute("side", isRTL ? "right" : "left");
-          }
+        // Returns whether the first float is smaller than the second float or
+        // equals to it in a range of epsilon.
+        function smallerTo(aFloat1, aFloat2, aEpsilon)
+        {
+          return aFloat1 <= (aFloat2 + aEpsilon);
         }
-        else if (position.indexOf("before_") == 0 || position.indexOf("after_") == 0) {
+
+        let popupRect = this.getBoundingClientRect();
+        let popupLeft = window.mozInnerScreenX + popupRect.left;
+        let popupTop = window.mozInnerScreenY + popupRect.top;
+        let popupRight = popupLeft + popupRect.width;
+        let popupBottom = popupTop + popupRect.height;
+
+        let anchorRect = anchor.getBoundingClientRect();
+        let anchorLeft = anchor.ownerDocument.defaultView.mozInnerScreenX + anchorRect.left;
+        let anchorTop = anchor.ownerDocument.defaultView.mozInnerScreenY + anchorRect.top;
+        let anchorRight = anchorLeft + anchorRect.width;
+        let anchorBottom = anchorTop + anchorRect.height;
+
+        try {
+          let anchorWindow = anchor.ownerDocument.defaultView;
+          if (anchorWindow != window) {
+            let utils = anchorWindow.QueryInterface(Components.interfaces.nsIInterfaceRequestor).
+                                     getInterface(Components.interfaces.nsIDOMWindowUtils);
+            let spp = utils.screenPixelsPerCSSPixel;
+            anchorLeft *= spp;
+            anchorRight *= spp;
+            anchorTop *= spp;
+            anchorBottom *= spp;
+          }
+        } catch(ex) { }
+
+        const epsilon = 0.2;
+
+        var horizPos = smallerTo(popupRight, anchorLeft, epsilon) ? -1 : smallerTo(anchorRight, popupLeft, epsilon) ? 1 : 0;
+        var vertPos = smallerTo(popupBottom, anchorTop, epsilon) ? -1 : smallerTo(anchorBottom, popupTop, epsilon) ? 1 : 0;
+
+        var anchorClass = "";
+        var hideAnchor = false;
+        if (horizPos == 0) {
           container.orient = "vertical";
           arrowbox.orient = "";
-          arrowbox.pack = (position.indexOf("_end") > 0) ? "end" : "start";
-
-          if (position.indexOf("before_") == 0) {
-            container.dir = "reverse";
-            this.setAttribute("side", "bottom");
+          if (vertPos == 0) {
+            hideAnchor = true;
           }
           else {
-            container.dir = "";
-            this.setAttribute("side", "top");
+            let pack = "";
+
+            // We have to guess where to position the arrow given that we don't
+            // have access to the parameters passed to |openPopup|.
+
+            // If the popup is on the left of the anchor.
+            if (smallerTo(popupLeft, anchorLeft, epsilon) && smallerTo(popupRight, anchorRight, epsilon)) {
+              pack = "end";
+            // If the popup is on the right of the anchor.
+            } else if (smallerTo(anchorLeft, popupLeft, epsilon) && smallerTo(anchorRight, popupRight, epsilon)) {
+              pack = "start"; //(popupLeft + popupRect.width / 2 > anchorRight) ? "start" : "end";
+            // If the popup is not on the right nor on the left.
+            // Basically, that means one is above the other and one is bigger
+            // than the other.
+            // In that case, we can't easily choose a position for the arrow so
+            // we have to guess depending on which side the popup is more close to.
+            } else {
+              pack = (Math.abs(popupLeft - anchorLeft) < Math.abs(popupRight - anchorRight)) ? "start" : "end";
+            }
+
+            // In RTL, everything should be inverted.
+            if (window.getComputedStyle(this).direction == "rtl") {
+              pack = (pack == "start") ? "end" : "start";
+            }
+
+            arrowbox.pack = pack;
+
+            if (vertPos == 1) {
+              container.dir = "";
+              anchorClass = "top";
+            }
+            else if (vertPos == -1) {
+              container.dir = "reverse"; 
+              anchorClass = "bottom";
+            }
           }
         }
-
-        arrow.hidden = false;
+        else if (vertPos == 0) {
+          container.orient = "";
+          arrowbox.orient = "vertical";
+          if (horizPos == 0) {
+            hideAnchor = true;
+          }
+          else {
+            let dir = "";
+            arrowbox.pack = popupTop + popupRect.height / 2 < anchorTop ? "end" : "start";
+            if (horizPos == 1) {
+              anchorClass = "left";
+            }
+            else if (horizPos == -1) {
+              dir = "reverse";
+              anchorClass = "right";
+            }
+            // In RTL, everything should be inverted.
+            if (window.getComputedStyle(this).direction == "rtl") {
+              dir = (dir == "") ? "reverse" : "";
+            }
+            container.dir = dir;
+          }
+        }
+        else {
+          hideAnchor = true;
+        }
+        arrow.hidden = hideAnchor;
+        arrow.setAttribute("side", anchorClass);
+        this.setAttribute("side", anchorClass);
 
         // set fading
         var fade = this.getAttribute("fade");