diff --git a/content/base/public/Element.h b/content/base/public/Element.h
index 10ee69a8c77..f94f8850b17 100644
--- a/content/base/public/Element.h
+++ b/content/base/public/Element.h
@@ -338,6 +338,8 @@ public:
             (HasValidDir() || IsHTML(nsGkAtoms::bdi)));
   }
 
+  Directionality GetComputedDirectionality() const;
+
 protected:
   /**
    * Method to get the _intrinsic_ content state of this element.  This is the
diff --git a/content/base/src/Element.cpp b/content/base/src/Element.cpp
index 6e52fe6e41c..1206848b3eb 100644
--- a/content/base/src/Element.cpp
+++ b/content/base/src/Element.cpp
@@ -3419,6 +3419,18 @@ Element::SetBoolAttr(nsIAtom* aAttr, bool aValue)
   return UnsetAttr(kNameSpaceID_None, aAttr, true);
 }
 
+Directionality
+Element::GetComputedDirectionality() const
+{
+  nsIFrame* frame = GetPrimaryFrame();
+  if (frame) {
+    return frame->StyleVisibility()->mDirection == NS_STYLE_DIRECTION_LTR
+             ? eDir_LTR : eDir_RTL;
+  }
+
+  return GetDirectionality();
+}
+
 float
 Element::FontSizeInflation()
 {
diff --git a/content/html/content/src/HTMLInputElement.cpp b/content/html/content/src/HTMLInputElement.cpp
index 40c205e6a8b..91340235ddb 100644
--- a/content/html/content/src/HTMLInputElement.cpp
+++ b/content/html/content/src/HTMLInputElement.cpp
@@ -2839,17 +2839,6 @@ SelectTextFieldOnFocus()
   return gSelectTextFieldOnFocus == 1;
 }
 
-static bool
-IsLTR(Element* aElement)
-{
-  nsIFrame* frame = aElement->GetPrimaryFrame();
-  if (frame) {
-    return frame->StyleVisibility()->mDirection == NS_STYLE_DIRECTION_LTR;
-  }
-  // at least for HTML, directionality is exclusively LTR or RTL
-  return aElement->GetDirectionality() == eDir_LTR;
-}
-
 bool
 HTMLInputElement::ShouldPreventDOMActivateDispatch(EventTarget* aOriginalTarget)
 {
@@ -3180,10 +3169,12 @@ HTMLInputElement::PostHandleEvent(nsEventChainPostVisitor& aVisitor)
               Decimal newValue;
               switch (keyEvent->keyCode) {
                 case  NS_VK_LEFT:
-                  newValue = value + (IsLTR(this) ? -step : step);
+                  newValue = value + (GetComputedDirectionality() == eDir_RTL
+                                        ? step : -step);
                   break;
                 case  NS_VK_RIGHT:
-                  newValue = value + (IsLTR(this) ? step : -step);
+                  newValue = value + (GetComputedDirectionality() == eDir_RTL
+                                        ? -step : step);
                   break;
                 case  NS_VK_UP:
                   // Even for horizontal range, "up" means "increase"