diff --git a/dom/animation/KeyframeEffect.cpp b/dom/animation/KeyframeEffect.cpp
index c8760b8de327..1a6c901a34b1 100644
--- a/dom/animation/KeyframeEffect.cpp
+++ b/dom/animation/KeyframeEffect.cpp
@@ -1277,8 +1277,8 @@ bool KeyframeEffect::CanThrottleOverflowChangesInScrollable(
   }
 
   ScrollStyles ss = scrollable->GetScrollStyles();
-  if (ss.mVertical == NS_STYLE_OVERFLOW_HIDDEN &&
-      ss.mHorizontal == NS_STYLE_OVERFLOW_HIDDEN &&
+  if (ss.mVertical == StyleOverflow::Hidden &&
+      ss.mHorizontal == StyleOverflow::Hidden &&
       scrollable->GetLogicalScrollPosition() == nsPoint(0, 0)) {
     return true;
   }
diff --git a/dom/base/nsDocument.cpp b/dom/base/nsDocument.cpp
index 0f047107f641..e60a50c85707 100644
--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -6995,7 +6995,7 @@ void nsIDocument::UpdateViewportOverflowType(nscoord aScrolledWidth,
   MOZ_ASSERT(mPresShell);
   nsPresContext* pc = GetPresContext();
   MOZ_ASSERT(pc->GetViewportScrollStylesOverride().mHorizontal ==
-                 NS_STYLE_OVERFLOW_HIDDEN,
+                 StyleOverflow::Hidden,
              "Should only be called when viewport has overflow-x: hidden");
   MOZ_ASSERT(aScrolledWidth > aScrollportWidth,
              "Should only be called when viewport is overflowed");
@@ -9317,15 +9317,15 @@ bool nsIDocument::IsPotentiallyScrollable(HTMLBodyElement* aBody) {
   MOZ_ASSERT(aBody->GetParent() == aBody->OwnerDoc()->GetRootElement());
   nsIFrame* parentFrame = aBody->GetParent()->GetPrimaryFrame();
   if (parentFrame &&
-      parentFrame->StyleDisplay()->mOverflowX == NS_STYLE_OVERFLOW_VISIBLE &&
-      parentFrame->StyleDisplay()->mOverflowY == NS_STYLE_OVERFLOW_VISIBLE) {
+      parentFrame->StyleDisplay()->mOverflowX == StyleOverflow::Visible &&
+      parentFrame->StyleDisplay()->mOverflowY == StyleOverflow::Visible) {
     return false;
   }
 
   // The element's used value of the overflow-x or overflow-y properties is not
   // visible.
-  if (bodyFrame->StyleDisplay()->mOverflowX == NS_STYLE_OVERFLOW_VISIBLE &&
-      bodyFrame->StyleDisplay()->mOverflowY == NS_STYLE_OVERFLOW_VISIBLE) {
+  if (bodyFrame->StyleDisplay()->mOverflowX == StyleOverflow::Visible &&
+      bodyFrame->StyleDisplay()->mOverflowY == StyleOverflow::Visible) {
     return false;
   }
 
diff --git a/dom/events/EventStateManager.cpp b/dom/events/EventStateManager.cpp
index f7eb98bbf24a..2ae6219c46da 100644
--- a/dom/events/EventStateManager.cpp
+++ b/dom/events/EventStateManager.cpp
@@ -2476,8 +2476,8 @@ nsIFrame* EventStateManager::ComputeScrollTargetAndMayAdjustWheelEvent(
     }
 
     ScrollStyles ss = scrollableFrame->GetScrollStyles();
-    bool hiddenForV = (NS_STYLE_OVERFLOW_HIDDEN == ss.mVertical);
-    bool hiddenForH = (NS_STYLE_OVERFLOW_HIDDEN == ss.mHorizontal);
+    bool hiddenForV = (StyleOverflow::Hidden == ss.mVertical);
+    bool hiddenForH = (StyleOverflow::Hidden == ss.mHorizontal);
     if ((hiddenForV && hiddenForH) ||
         (checkIfScrollableY && !checkIfScrollableX && hiddenForV) ||
         (checkIfScrollableX && !checkIfScrollableY && hiddenForH)) {
@@ -2585,10 +2585,10 @@ void EventStateManager::DoScrollText(nsIScrollableFrame* aScrollableFrame,
 
   // Don't scroll around the axis whose overflow style is hidden.
   ScrollStyles overflowStyle = aScrollableFrame->GetScrollStyles();
-  if (overflowStyle.mHorizontal == NS_STYLE_OVERFLOW_HIDDEN) {
+  if (overflowStyle.mHorizontal == StyleOverflow::Hidden) {
     actualDevPixelScrollAmount.x = 0;
   }
-  if (overflowStyle.mVertical == NS_STYLE_OVERFLOW_HIDDEN) {
+  if (overflowStyle.mVertical == StyleOverflow::Hidden) {
     actualDevPixelScrollAmount.y = 0;
   }
 
@@ -2688,15 +2688,13 @@ void EventStateManager::DoScrollText(nsIScrollableFrame* aScrollableFrame,
   // additional action such as moving history.  In such case, overflowDelta
   // values should stay zero.
   if (scrollFrameWeak.IsAlive()) {
-    if (aEvent->mDeltaX &&
-        overflowStyle.mHorizontal == NS_STYLE_OVERFLOW_HIDDEN &&
+    if (aEvent->mDeltaX && overflowStyle.mHorizontal == StyleOverflow::Hidden &&
         !ComputeScrollTargetAndMayAdjustWheelEvent(
             scrollFrame, aEvent,
             COMPUTE_SCROLLABLE_ANCESTOR_ALONG_X_AXIS_WITH_AUTO_DIR)) {
       aEvent->mOverflowDeltaX = aEvent->mDeltaX;
     }
-    if (aEvent->mDeltaY &&
-        overflowStyle.mVertical == NS_STYLE_OVERFLOW_HIDDEN &&
+    if (aEvent->mDeltaY && overflowStyle.mVertical == StyleOverflow::Hidden &&
         !ComputeScrollTargetAndMayAdjustWheelEvent(
             scrollFrame, aEvent,
             COMPUTE_SCROLLABLE_ANCESTOR_ALONG_Y_AXIS_WITH_AUTO_DIR)) {
diff --git a/gfx/layers/apz/util/APZCCallbackHelper.cpp b/gfx/layers/apz/util/APZCCallbackHelper.cpp
index 09046c94a70e..8b20322d964a 100644
--- a/gfx/layers/apz/util/APZCCallbackHelper.cpp
+++ b/gfx/layers/apz/util/APZCCallbackHelper.cpp
@@ -121,7 +121,7 @@ static CSSPoint ScrollFrameTo(nsIScrollableFrame* aFrame,
   // overflow:hidden (that is, we take |targetScrollPosition|). If this turns
   // out to be problematic, an alternative solution would be to ignore the
   // scroll position change (that is, use |geckoScrollPosition|).
-  if (aFrame->GetScrollStyles().mVertical == NS_STYLE_OVERFLOW_HIDDEN &&
+  if (aFrame->GetScrollStyles().mVertical == StyleOverflow::Hidden &&
       targetScrollPosition.y != geckoScrollPosition.y) {
     NS_WARNING(
         nsPrintfCString(
@@ -129,7 +129,7 @@ static CSSPoint ScrollFrameTo(nsIScrollableFrame* aFrame,
             targetScrollPosition.y, geckoScrollPosition.y)
             .get());
   }
-  if (aFrame->GetScrollStyles().mHorizontal == NS_STYLE_OVERFLOW_HIDDEN &&
+  if (aFrame->GetScrollStyles().mHorizontal == StyleOverflow::Hidden &&
       targetScrollPosition.x != geckoScrollPosition.x) {
     NS_WARNING(
         nsPrintfCString(
diff --git a/layout/base/PresShell.cpp b/layout/base/PresShell.cpp
index bb9916267fe7..1fa2031e9741 100644
--- a/layout/base/PresShell.cpp
+++ b/layout/base/PresShell.cpp
@@ -3264,7 +3264,7 @@ static void ScrollToShowRect(nsIScrollableFrame* aFrameAsScrollable,
   uint32_t directions = aFrameAsScrollable->GetPerceivedScrollingDirections();
 
   if (((aFlags & nsIPresShell::SCROLL_OVERFLOW_HIDDEN) ||
-       ss.mVertical != NS_STYLE_OVERFLOW_HIDDEN) &&
+       ss.mVertical != StyleOverflow::Hidden) &&
       (!aVertical.mOnlyIfPerceivedScrollableDirection ||
        (directions & nsIScrollableFrame::VERTICAL))) {
     if (ComputeNeedToScroll(aVertical.mWhenToScroll, lineSize.height, aRect.y,
@@ -3280,7 +3280,7 @@ static void ScrollToShowRect(nsIScrollableFrame* aFrameAsScrollable,
   }
 
   if (((aFlags & nsIPresShell::SCROLL_OVERFLOW_HIDDEN) ||
-       ss.mHorizontal != NS_STYLE_OVERFLOW_HIDDEN) &&
+       ss.mHorizontal != StyleOverflow::Hidden) &&
       (!aHorizontal.mOnlyIfPerceivedScrollableDirection ||
        (directions & nsIScrollableFrame::HORIZONTAL))) {
     if (ComputeNeedToScroll(aHorizontal.mWhenToScroll, lineSize.width, aRect.x,
diff --git a/layout/base/ScrollStyles.cpp b/layout/base/ScrollStyles.cpp
index 2b8f45356f5a..12c34154121e 100644
--- a/layout/base/ScrollStyles.cpp
+++ b/layout/base/ScrollStyles.cpp
@@ -9,7 +9,7 @@
 
 namespace mozilla {
 
-ScrollStyles::ScrollStyles(uint8_t aH, uint8_t aV,
+ScrollStyles::ScrollStyles(StyleOverflow aH, StyleOverflow aV,
                            const nsStyleDisplay* aDisplay)
     : mHorizontal(aH),
       mVertical(aV),
diff --git a/layout/base/ScrollStyles.h b/layout/base/ScrollStyles.h
index c12b554ac67b..30c6ebc23a74 100644
--- a/layout/base/ScrollStyles.h
+++ b/layout/base/ScrollStyles.h
@@ -18,30 +18,29 @@ struct nsStyleDisplay;
 namespace mozilla {
 
 struct ScrollStyles {
-  // Always one of NS_STYLE_OVERFLOW_SCROLL, NS_STYLE_OVERFLOW_HIDDEN,
-  // or NS_STYLE_OVERFLOW_AUTO.
-  uint8_t mHorizontal;
-  uint8_t mVertical;
+  // Always one of Scroll, Hidden, or Auto
+  StyleOverflow mHorizontal;
+  StyleOverflow mVertical;
   // Always one of NS_STYLE_SCROLL_BEHAVIOR_AUTO or
   // NS_STYLE_SCROLL_BEHAVIOR_SMOOTH
   uint8_t mScrollBehavior;
-  mozilla::StyleOverscrollBehavior mOverscrollBehaviorX;
-  mozilla::StyleOverscrollBehavior mOverscrollBehaviorY;
-  mozilla::StyleScrollSnapType mScrollSnapTypeX;
-  mozilla::StyleScrollSnapType mScrollSnapTypeY;
+  StyleOverscrollBehavior mOverscrollBehaviorX;
+  StyleOverscrollBehavior mOverscrollBehaviorY;
+  StyleScrollSnapType mScrollSnapTypeX;
+  StyleScrollSnapType mScrollSnapTypeY;
   nsStyleCoord mScrollSnapPointsX;
   nsStyleCoord mScrollSnapPointsY;
   nsStyleCoord::CalcValue mScrollSnapDestinationX;
   nsStyleCoord::CalcValue mScrollSnapDestinationY;
 
-  ScrollStyles(uint8_t aH, uint8_t aV)
+  ScrollStyles(StyleOverflow aH, StyleOverflow aV)
       : mHorizontal(aH),
         mVertical(aV),
         mScrollBehavior(NS_STYLE_SCROLL_BEHAVIOR_AUTO),
         mOverscrollBehaviorX(StyleOverscrollBehavior::Auto),
         mOverscrollBehaviorY(StyleOverscrollBehavior::Auto),
-        mScrollSnapTypeX(mozilla::StyleScrollSnapType::None),
-        mScrollSnapTypeY(mozilla::StyleScrollSnapType::None),
+        mScrollSnapTypeX(StyleScrollSnapType::None),
+        mScrollSnapTypeY(StyleScrollSnapType::None),
         mScrollSnapPointsX(nsStyleCoord(eStyleUnit_None)),
         mScrollSnapPointsY(nsStyleCoord(eStyleUnit_None)) {
     mScrollSnapDestinationX.mPercent = 0;
@@ -53,7 +52,7 @@ struct ScrollStyles {
   }
 
   explicit ScrollStyles(const nsStyleDisplay* aDisplay);
-  ScrollStyles(uint8_t aH, uint8_t aV, const nsStyleDisplay* aDisplay);
+  ScrollStyles(StyleOverflow aH, StyleOverflow aV, const nsStyleDisplay*);
   bool operator==(const ScrollStyles& aStyles) const {
     return aStyles.mHorizontal == mHorizontal &&
            aStyles.mVertical == mVertical &&
@@ -71,8 +70,8 @@ struct ScrollStyles {
     return !(*this == aStyles);
   }
   bool IsHiddenInBothDirections() const {
-    return mHorizontal == NS_STYLE_OVERFLOW_HIDDEN &&
-           mVertical == NS_STYLE_OVERFLOW_HIDDEN;
+    return mHorizontal == StyleOverflow::Hidden &&
+           mVertical == StyleOverflow::Hidden;
   }
   bool IsSmoothScroll(dom::ScrollBehavior aBehavior) const {
     return aBehavior == dom::ScrollBehavior::Smooth ||
diff --git a/layout/base/nsLayoutUtils.cpp b/layout/base/nsLayoutUtils.cpp
index 10af5c03dab9..7cf4d0535419 100644
--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -1827,9 +1827,9 @@ nsIScrollableFrame* nsLayoutUtils::GetNearestScrollableFrameForDirection(
       ScrollStyles ss = scrollableFrame->GetScrollStyles();
       uint32_t directions = scrollableFrame->GetPerceivedScrollingDirections();
       if (aDirection == eVertical
-              ? (ss.mVertical != NS_STYLE_OVERFLOW_HIDDEN &&
+              ? (ss.mVertical != StyleOverflow::Hidden &&
                  (directions & nsIScrollableFrame::VERTICAL))
-              : (ss.mHorizontal != NS_STYLE_OVERFLOW_HIDDEN &&
+              : (ss.mHorizontal != StyleOverflow::Hidden &&
                  (directions & nsIScrollableFrame::HORIZONTAL)))
         return scrollableFrame;
     }
@@ -1854,8 +1854,8 @@ nsIScrollableFrame* nsLayoutUtils::GetNearestScrollableFrame(nsIFrame* aFrame,
       } else {
         ScrollStyles ss = scrollableFrame->GetScrollStyles();
         if ((aFlags & SCROLLABLE_INCLUDE_HIDDEN) ||
-            ss.mVertical != NS_STYLE_OVERFLOW_HIDDEN ||
-            ss.mHorizontal != NS_STYLE_OVERFLOW_HIDDEN) {
+            ss.mVertical != StyleOverflow::Hidden ||
+            ss.mHorizontal != StyleOverflow::Hidden) {
           return scrollableFrame;
         }
       }
@@ -5386,7 +5386,7 @@ static void AddStateBitToAncestors(nsIFrame* aFrame, nsFrameState aBit) {
   nscoord* fixedMinSize = nullptr;
   auto minSizeUnit = size.GetUnit();
   if (minSizeUnit == eStyleUnit_Auto) {
-    if (aFrame->StyleDisplay()->mOverflowX == NS_STYLE_OVERFLOW_VISIBLE) {
+    if (aFrame->StyleDisplay()->mOverflowX == StyleOverflow::Visible) {
       size = aAxis == eAxisHorizontal ? stylePos->mWidth : stylePos->mHeight;
       // This is same as above: keywords should behaves as property's initial
       // values in block axis.
@@ -8339,12 +8339,12 @@ nsLayoutUtils::ScrollbarAreaToExcludeFromCompositionBoundsFor(
 
     nsPoint scrollPosition = aScrollableFrame->GetScrollPosition();
     if (aScrollableFrame->GetScrollStyles().mVertical ==
-        NS_STYLE_OVERFLOW_HIDDEN) {
+        StyleOverflow::Hidden) {
       contentBounds.y = scrollPosition.y;
       contentBounds.height = 0;
     }
     if (aScrollableFrame->GetScrollStyles().mHorizontal ==
-        NS_STYLE_OVERFLOW_HIDDEN) {
+        StyleOverflow::Hidden) {
       contentBounds.x = scrollPosition.x;
       contentBounds.width = 0;
     }
diff --git a/layout/base/nsPresContext.cpp b/layout/base/nsPresContext.cpp
index 3cb15d2d036d..81ad2d640988 100644
--- a/layout/base/nsPresContext.cpp
+++ b/layout/base/nsPresContext.cpp
@@ -193,7 +193,7 @@ nsPresContext::nsPresContext(nsIDocument* aDocument, nsPresContextType aType)
       mFocusTextColor(mDefaultColor),
       mBodyTextColor(mDefaultColor),
       mViewportScrollOverrideElement(nullptr),
-      mViewportScrollStyles(NS_STYLE_OVERFLOW_AUTO, NS_STYLE_OVERFLOW_AUTO),
+      mViewportScrollStyles(StyleOverflow::Auto, StyleOverflow::Auto),
       mFocusRingWidth(1),
       mExistThrottledUpdates(false),
       // mImageAnimationMode is initialised below, in constructor body
@@ -1240,7 +1240,7 @@ gfxSize nsPresContext::ScreenSizeInchesForFontInflation(bool* aChanged) {
 
 static bool CheckOverflow(const nsStyleDisplay* aDisplay,
                           ScrollStyles* aStyles) {
-  if (aDisplay->mOverflowX == NS_STYLE_OVERFLOW_VISIBLE &&
+  if (aDisplay->mOverflowX == StyleOverflow::Visible &&
       aDisplay->mScrollBehavior == NS_STYLE_SCROLL_BEHAVIOR_AUTO &&
       aDisplay->mOverscrollBehaviorX == StyleOverscrollBehavior::Auto &&
       aDisplay->mOverscrollBehaviorY == StyleOverscrollBehavior::Auto &&
@@ -1255,9 +1255,9 @@ static bool CheckOverflow(const nsStyleDisplay* aDisplay,
     return false;
   }
 
-  if (aDisplay->mOverflowX == NS_STYLE_OVERFLOW_CLIP) {
-    *aStyles = ScrollStyles(NS_STYLE_OVERFLOW_HIDDEN, NS_STYLE_OVERFLOW_HIDDEN,
-                            aDisplay);
+  if (aDisplay->mOverflowX == StyleOverflow::MozHiddenUnscrollable) {
+    *aStyles =
+        ScrollStyles(StyleOverflow::Hidden, StyleOverflow::Hidden, aDisplay);
   } else {
     *aStyles = ScrollStyles(aDisplay);
   }
@@ -1315,7 +1315,7 @@ static Element* GetPropagatedScrollStylesForViewport(
 Element* nsPresContext::UpdateViewportScrollStylesOverride() {
   // Start off with our default styles, and then update them as needed.
   mViewportScrollStyles =
-      ScrollStyles(NS_STYLE_OVERFLOW_AUTO, NS_STYLE_OVERFLOW_AUTO);
+      ScrollStyles(StyleOverflow::Auto, StyleOverflow::Auto);
   mViewportScrollOverrideElement = nullptr;
   // Don't propagate the scrollbar state in printing or print preview.
   if (!IsPaginated()) {
@@ -1333,7 +1333,7 @@ Element* nsPresContext::UpdateViewportScrollStylesOverride() {
     if (fullscreenElement != document->GetRootElement() &&
         fullscreenElement != mViewportScrollOverrideElement) {
       mViewportScrollStyles =
-          ScrollStyles(NS_STYLE_OVERFLOW_HIDDEN, NS_STYLE_OVERFLOW_HIDDEN);
+          ScrollStyles(StyleOverflow::Hidden, StyleOverflow::Hidden);
     }
   }
   return mViewportScrollOverrideElement;
@@ -1351,7 +1351,7 @@ bool nsPresContext::ElementWouldPropagateScrollStyles(const Element& aElement) {
   // but saves us having to have more complicated code or more code duplication;
   // in practice we will make this call quite rarely, because we checked for all
   // the common cases above.
-  ScrollStyles dummy(NS_STYLE_OVERFLOW_AUTO, NS_STYLE_OVERFLOW_AUTO);
+  ScrollStyles dummy(StyleOverflow::Auto, StyleOverflow::Auto);
   return GetPropagatedScrollStylesForViewport(this, &dummy) == &aElement;
 }
 
diff --git a/layout/forms/nsHTMLButtonControlFrame.cpp b/layout/forms/nsHTMLButtonControlFrame.cpp
index 8a983c45052a..5d955010ad10 100644
--- a/layout/forms/nsHTMLButtonControlFrame.cpp
+++ b/layout/forms/nsHTMLButtonControlFrame.cpp
@@ -72,7 +72,7 @@ nsresult nsHTMLButtonControlFrame::HandleEvent(nsPresContext* aPresContext,
 }
 
 bool nsHTMLButtonControlFrame::ShouldClipPaintingToBorderBox() {
-  return IsInput() || StyleDisplay()->mOverflowX != NS_STYLE_OVERFLOW_VISIBLE;
+  return IsInput() || StyleDisplay()->mOverflowX != StyleOverflow::Visible;
 }
 
 void nsHTMLButtonControlFrame::BuildDisplayList(
diff --git a/layout/forms/nsListControlFrame.cpp b/layout/forms/nsListControlFrame.cpp
index 3c34ed830349..eb3365b3532f 100644
--- a/layout/forms/nsListControlFrame.cpp
+++ b/layout/forms/nsListControlFrame.cpp
@@ -602,12 +602,11 @@ void nsListControlFrame::ReflowAsDropdown(nsPresContext* aPresContext,
 ScrollStyles nsListControlFrame::GetScrollStyles() const {
   // We can't express this in the style system yet; when we can, this can go
   // away and GetScrollStyles can be devirtualized
-  int32_t style =
-      IsInDropDownMode() ? NS_STYLE_OVERFLOW_AUTO : NS_STYLE_OVERFLOW_SCROLL;
+  auto style = IsInDropDownMode() ? StyleOverflow::Auto : StyleOverflow::Scroll;
   if (GetWritingMode().IsVertical()) {
-    return ScrollStyles(style, NS_STYLE_OVERFLOW_HIDDEN);
+    return ScrollStyles(style, StyleOverflow::Hidden);
   } else {
-    return ScrollStyles(NS_STYLE_OVERFLOW_HIDDEN, style);
+    return ScrollStyles(StyleOverflow::Hidden, style);
   }
 }
 
diff --git a/layout/forms/nsTextControlFrame.cpp b/layout/forms/nsTextControlFrame.cpp
index 80caca56a5b6..8cfa8939c2ce 100644
--- a/layout/forms/nsTextControlFrame.cpp
+++ b/layout/forms/nsTextControlFrame.cpp
@@ -443,11 +443,11 @@ nsresult nsTextControlFrame::CreateRootNode() {
   if (!IsSingleLineTextControl()) {
     // We can't just inherit the overflow because setting visible overflow will
     // crash when the number of lines exceeds the height of the textarea and
-    // setting -moz-hidden-unscrollable overflow (NS_STYLE_OVERFLOW_CLIP)
-    // doesn't paint the caret for some reason.
+    // setting -moz-hidden-unscrollable overflow doesn't paint the caret for
+    // some reason.
     const nsStyleDisplay* disp = StyleDisplay();
-    if (disp->mOverflowX != NS_STYLE_OVERFLOW_VISIBLE &&
-        disp->mOverflowX != NS_STYLE_OVERFLOW_CLIP) {
+    if (disp->mOverflowX != StyleOverflow::Visible &&
+        disp->mOverflowX != StyleOverflow::MozHiddenUnscrollable) {
       classValue.AppendLiteral(" inherit-overflow");
     }
   }
diff --git a/layout/generic/ReflowInput.cpp b/layout/generic/ReflowInput.cpp
index f57aab452755..e3c2b2925789 100644
--- a/layout/generic/ReflowInput.cpp
+++ b/layout/generic/ReflowInput.cpp
@@ -407,7 +407,7 @@ void ReflowInput::Init(nsPresContext* aPresContext,
   nsIFrame* parent = mFrame->GetParent();
   if (parent && (parent->GetStateBits() & NS_FRAME_IN_CONSTRAINED_BSIZE) &&
       !(parent->IsScrollFrame() &&
-        parent->StyleDisplay()->mOverflowY != NS_STYLE_OVERFLOW_HIDDEN)) {
+        parent->StyleDisplay()->mOverflowY != StyleOverflow::Hidden)) {
     mFrame->AddStateBits(NS_FRAME_IN_CONSTRAINED_BSIZE);
   } else if (type == LayoutFrameType::SVGForeignObject) {
     // An SVG foreignObject frame is inherently constrained block-size.
diff --git a/layout/generic/TextOverflow.cpp b/layout/generic/TextOverflow.cpp
index 946995b0dc6d..9d6840de4f75 100644
--- a/layout/generic/TextOverflow.cpp
+++ b/layout/generic/TextOverflow.cpp
@@ -102,7 +102,7 @@ static bool IsInlineAxisOverflowVisible(nsIFrame* aFrame) {
   auto overflow = aFrame->GetWritingMode().IsVertical()
                       ? f->StyleDisplay()->mOverflowY
                       : f->StyleDisplay()->mOverflowX;
-  return overflow == NS_STYLE_OVERFLOW_VISIBLE;
+  return overflow == StyleOverflow::Visible;
 }
 
 static void ClipMarker(const nsRect& aContentArea, const nsRect& aMarkerRect,
@@ -314,7 +314,7 @@ TextOverflow::TextOverflow(nsDisplayListBuilder* aBuilder,
     auto scrollbarStyle = mBlockWM.IsVertical()
                               ? mScrollableFrame->GetScrollStyles().mVertical
                               : mScrollableFrame->GetScrollStyles().mHorizontal;
-    mCanHaveInlineAxisScrollbar = scrollbarStyle != NS_STYLE_OVERFLOW_HIDDEN;
+    mCanHaveInlineAxisScrollbar = scrollbarStyle != StyleOverflow::Hidden;
     if (!mAdjustForPixelSnapping) {
       // Scrolling to the end position can leave some text still overflowing due
       // to pixel snapping behaviour in our scrolling code.
diff --git a/layout/generic/nsFlexContainerFrame.cpp b/layout/generic/nsFlexContainerFrame.cpp
index 04fa2b648013..1e5ab1556e78 100644
--- a/layout/generic/nsFlexContainerFrame.cpp
+++ b/layout/generic/nsFlexContainerFrame.cpp
@@ -2036,7 +2036,7 @@ void FlexItem::CheckForMinSizeAuto(const ReflowInput& aFlexItemReflowInput,
   // non-'visible' due to the way the subproperties interact.
   mNeedsMinSizeAutoResolution =
       IsAutoOrEnumOnBSize(mainMinSize, IsInlineAxisMainAxis()) &&
-      disp->mOverflowX == NS_STYLE_OVERFLOW_VISIBLE;
+      disp->mOverflowX == StyleOverflow::Visible;
 }
 
 nscoord FlexItem::GetBaselineOffsetFromOuterCrossEdge(
diff --git a/layout/generic/nsFrame.cpp b/layout/generic/nsFrame.cpp
index 33ab05e55fad..4a5046576cf4 100644
--- a/layout/generic/nsFrame.cpp
+++ b/layout/generic/nsFrame.cpp
@@ -8895,8 +8895,8 @@ bool nsIFrame::FinishAndStoreOverflow(nsOverflowAreas& aOverflowAreas,
   // children are actually clipped to the padding-box, but since the
   // overflow area should include the entire border-box, just set it to
   // the border-box here.
-  NS_ASSERTION((disp->mOverflowY == NS_STYLE_OVERFLOW_CLIP) ==
-                   (disp->mOverflowX == NS_STYLE_OVERFLOW_CLIP),
+  NS_ASSERTION((disp->mOverflowY == StyleOverflow::MozHiddenUnscrollable) ==
+                   (disp->mOverflowX == StyleOverflow::MozHiddenUnscrollable),
                "If one overflow is clip, the other should be too");
   if (applyOverflowClipping) {
     // The contents are actually clipped to the padding area
@@ -8917,8 +8917,8 @@ bool nsIFrame::FinishAndStoreOverflow(nsOverflowAreas& aOverflowAreas,
     }
   }
 
-  // Note that NS_STYLE_OVERFLOW_CLIP doesn't clip the frame background,
-  // so we add theme background overflow here so it's not clipped.
+  // Note that StyleOverflow::MozHiddenUnscrollable doesn't clip the frame
+  // background, so we add theme background overflow here so it's not clipped.
   if (!::IsXULBoxWrapped(this) && IsThemed(disp)) {
     nsRect r(bounds);
     nsPresContext* presContext = PresContext();
diff --git a/layout/generic/nsFrame.h b/layout/generic/nsFrame.h
index 183e9c4fb05e..3c662795e373 100644
--- a/layout/generic/nsFrame.h
+++ b/layout/generic/nsFrame.h
@@ -588,7 +588,8 @@ class nsFrame : public nsBox {
                                           const nsStyleDisplay* aDisp) {
     // clip overflow:-moz-hidden-unscrollable, except for nsListControlFrame,
     // which is an nsHTMLScrollFrame.
-    if (MOZ_UNLIKELY(aDisp->mOverflowX == NS_STYLE_OVERFLOW_CLIP &&
+    if (MOZ_UNLIKELY(aDisp->mOverflowX ==
+                         mozilla::StyleOverflow::MozHiddenUnscrollable &&
                      !aFrame->IsListControlFrame())) {
       return true;
     }
@@ -603,8 +604,8 @@ class nsFrame : public nsBox {
     }
 
     // and overflow:hidden that we should interpret as -moz-hidden-unscrollable
-    if (aDisp->mOverflowX == NS_STYLE_OVERFLOW_HIDDEN &&
-        aDisp->mOverflowY == NS_STYLE_OVERFLOW_HIDDEN) {
+    if (aDisp->mOverflowX == mozilla::StyleOverflow::Hidden &&
+        aDisp->mOverflowY == mozilla::StyleOverflow::Hidden) {
       // REVIEW: these are the frame types that set up clipping.
       mozilla::LayoutFrameType type = aFrame->Type();
       if (type == mozilla::LayoutFrameType::Table ||
diff --git a/layout/generic/nsFrameSelection.cpp b/layout/generic/nsFrameSelection.cpp
index e5223a50a0df..9477dbf9af15 100644
--- a/layout/generic/nsFrameSelection.cpp
+++ b/layout/generic/nsFrameSelection.cpp
@@ -1613,7 +1613,7 @@ nsIFrame* nsFrameSelection::GetFrameToPageSelect() const {
         continue;
       }
       ScrollStyles scrollStyles = scrollableFrame->GetScrollStyles();
-      if (scrollStyles.mVertical == NS_STYLE_OVERFLOW_HIDDEN) {
+      if (scrollStyles.mVertical == StyleOverflow::Hidden) {
         continue;
       }
       uint32_t directions = scrollableFrame->GetPerceivedScrollingDirections();
diff --git a/layout/generic/nsGfxScrollFrame.cpp b/layout/generic/nsGfxScrollFrame.cpp
index 79e4a752ae24..e4fb8e10b901 100644
--- a/layout/generic/nsGfxScrollFrame.cpp
+++ b/layout/generic/nsGfxScrollFrame.cpp
@@ -189,14 +189,14 @@ enum class ShowScrollbar : uint8_t {
   Never,
 };
 
-static ShowScrollbar ShouldShowScrollbar(uint8_t aOverflow) {
+static ShowScrollbar ShouldShowScrollbar(StyleOverflow aOverflow) {
   switch (aOverflow) {
-    case NS_STYLE_OVERFLOW_SCROLL:
+    case StyleOverflow::Scroll:
       return ShowScrollbar::Always;
-    case NS_STYLE_OVERFLOW_HIDDEN:
+    case StyleOverflow::Hidden:
       return ShowScrollbar::Never;
     default:
-    case NS_STYLE_OVERFLOW_AUTO:
+    case StyleOverflow::Auto:
       return ShowScrollbar::Auto;
   }
 }
@@ -432,7 +432,7 @@ bool nsHTMLScrollFrame::TryLayout(ScrollReflowInput* aState,
     // care about what the page itself specifies.
     nsPresContext* pc = PresContext();
     ScrollStyles styles = pc->GetViewportScrollStylesOverride();
-    if (styles.mHorizontal != NS_STYLE_OVERFLOW_HIDDEN) {
+    if (styles.mHorizontal != StyleOverflow::Hidden) {
       break;
     }
     // Only top level content document is considered.
@@ -798,7 +798,7 @@ void nsHTMLScrollFrame::PlaceScrollArea(ScrollReflowInput& aState,
 nscoord nsHTMLScrollFrame::GetIntrinsicVScrollbarWidth(
     gfxContext* aRenderingContext) {
   ScrollStyles ss = GetScrollStyles();
-  if (ss.mVertical != NS_STYLE_OVERFLOW_SCROLL || !mHelper.mVScrollbarBox)
+  if (ss.mVertical != StyleOverflow::Scroll || !mHelper.mVScrollbarBox)
     return 0;
 
   // Don't need to worry about reflow depth here since it's
@@ -1310,9 +1310,9 @@ bool ScrollFrameHelper::WantAsyncScroll() const {
   }
 
   bool isVScrollable = (scrollRange.height >= oneDevPixel) &&
-                       (styles.mVertical != NS_STYLE_OVERFLOW_HIDDEN);
+                       (styles.mVertical != StyleOverflow::Hidden);
   bool isHScrollable = (scrollRange.width >= oneDevPixel) &&
-                       (styles.mHorizontal != NS_STYLE_OVERFLOW_HIDDEN);
+                       (styles.mHorizontal != StyleOverflow::Hidden);
 
 #if defined(MOZ_WIDGET_ANDROID)
   // Mobile platforms need focus to scroll text inputs.
@@ -1516,14 +1516,13 @@ nsSize nsXULScrollFrame::GetXULPrefSize(nsBoxLayoutState& aState) {
 
   // scrolled frames don't have their own margins
 
-  if (mHelper.mVScrollbarBox && styles.mVertical == NS_STYLE_OVERFLOW_SCROLL) {
+  if (mHelper.mVScrollbarBox && styles.mVertical == StyleOverflow::Scroll) {
     nsSize vSize = mHelper.mVScrollbarBox->GetXULPrefSize(aState);
     nsBox::AddMargin(mHelper.mVScrollbarBox, vSize);
     pref.width += vSize.width;
   }
 
-  if (mHelper.mHScrollbarBox &&
-      styles.mHorizontal == NS_STYLE_OVERFLOW_SCROLL) {
+  if (mHelper.mHScrollbarBox && styles.mHorizontal == StyleOverflow::Scroll) {
     nsSize hSize = mHelper.mHScrollbarBox->GetXULPrefSize(aState);
     nsBox::AddMargin(mHelper.mHScrollbarBox, hSize);
     pref.height += hSize.height;
@@ -1540,15 +1539,14 @@ nsSize nsXULScrollFrame::GetXULMinSize(nsBoxLayoutState& aState) {
 
   ScrollStyles styles = GetScrollStyles();
 
-  if (mHelper.mVScrollbarBox && styles.mVertical == NS_STYLE_OVERFLOW_SCROLL) {
+  if (mHelper.mVScrollbarBox && styles.mVertical == StyleOverflow::Scroll) {
     nsSize vSize = mHelper.mVScrollbarBox->GetXULMinSize(aState);
     AddMargin(mHelper.mVScrollbarBox, vSize);
     min.width += vSize.width;
     if (min.height < vSize.height) min.height = vSize.height;
   }
 
-  if (mHelper.mHScrollbarBox &&
-      styles.mHorizontal == NS_STYLE_OVERFLOW_SCROLL) {
+  if (mHelper.mHScrollbarBox && styles.mHorizontal == StyleOverflow::Scroll) {
     nsSize hSize = mHelper.mHScrollbarBox->GetXULMinSize(aState);
     AddMargin(mHelper.mHScrollbarBox, hSize);
     min.height += hSize.height;
@@ -2392,8 +2390,8 @@ bool ScrollFrameHelper::IsAlwaysActive() const {
   // If we're overflow:hidden, then start as inactive until
   // we get scrolled manually.
   ScrollStyles styles = GetScrollStylesFromFrame();
-  return (styles.mHorizontal != NS_STYLE_OVERFLOW_HIDDEN &&
-          styles.mVertical != NS_STYLE_OVERFLOW_HIDDEN);
+  return (styles.mHorizontal != StyleOverflow::Hidden &&
+          styles.mVertical != StyleOverflow::Hidden);
 }
 
 static void RemoveDisplayPortCallback(nsITimer* aTimer, void* aClosure) {
@@ -3876,7 +3874,7 @@ bool ScrollFrameHelper::IsRectNearlyVisible(const nsRect& aRect) const {
 }
 
 static void HandleScrollPref(nsIScrollable* aScrollable, int32_t aOrientation,
-                             uint8_t& aValue) {
+                             StyleOverflow& aValue) {
   int32_t pref;
   aScrollable->GetDefaultScrollbarPreferences(aOrientation, &pref);
   switch (pref) {
@@ -3884,10 +3882,10 @@ static void HandleScrollPref(nsIScrollable* aScrollable, int32_t aOrientation,
       // leave |aValue| untouched
       break;
     case nsIScrollable::Scrollbar_Never:
-      aValue = NS_STYLE_OVERFLOW_HIDDEN;
+      aValue = StyleOverflow::Hidden;
       break;
     case nsIScrollable::Scrollbar_Always:
-      aValue = NS_STYLE_OVERFLOW_SCROLL;
+      aValue = StyleOverflow::Scroll;
       break;
   }
 }
@@ -3896,7 +3894,7 @@ ScrollStyles ScrollFrameHelper::GetScrollStylesFromFrame() const {
   nsPresContext* presContext = mOuter->PresContext();
   if (!presContext->IsDynamic() &&
       !(mIsRoot && presContext->HasPaginatedScrolling())) {
-    return ScrollStyles(NS_STYLE_OVERFLOW_HIDDEN, NS_STYLE_OVERFLOW_HIDDEN);
+    return ScrollStyles(StyleOverflow::Hidden, StyleOverflow::Hidden);
   }
 
   if (!mIsRoot) {
@@ -4537,8 +4535,8 @@ nsresult ScrollFrameHelper::CreateAnonymousContent(
       canHaveVertical = false;
     } else {
       ScrollStyles styles = scrollable->GetScrollStyles();
-      canHaveHorizontal = styles.mHorizontal != NS_STYLE_OVERFLOW_HIDDEN;
-      canHaveVertical = styles.mVertical != NS_STYLE_OVERFLOW_HIDDEN;
+      canHaveHorizontal = styles.mHorizontal != StyleOverflow::Hidden;
+      canHaveVertical = styles.mVertical != StyleOverflow::Hidden;
     }
     if (!canHaveHorizontal && !canHaveVertical && !isResizable) {
       // Nothing to do.
@@ -5222,9 +5220,9 @@ nsresult nsXULScrollFrame::XULLayout(nsBoxLayoutState& aState) {
   ScrollStyles styles = GetScrollStyles();
 
   // Look at our style do we always have vertical or horizontal scrollbars?
-  if (styles.mHorizontal == NS_STYLE_OVERFLOW_SCROLL)
+  if (styles.mHorizontal == StyleOverflow::Scroll)
     mHelper.mHasHorizontalScrollbar = true;
-  if (styles.mVertical == NS_STYLE_OVERFLOW_SCROLL)
+  if (styles.mVertical == StyleOverflow::Scroll)
     mHelper.mHasVerticalScrollbar = true;
 
   if (mHelper.mHasHorizontalScrollbar)
@@ -5240,13 +5238,13 @@ nsresult nsXULScrollFrame::XULLayout(nsBoxLayoutState& aState) {
   bool needsLayout = false;
 
   // if we have 'auto' scrollbars look at the vertical case
-  if (styles.mVertical != NS_STYLE_OVERFLOW_SCROLL) {
+  if (styles.mVertical != StyleOverflow::Scroll) {
     // These are only good until the call to LayoutScrollArea.
     nsRect scrolledRect = mHelper.GetScrolledRect();
 
     // There are two cases to consider
     if (scrolledRect.height <= mHelper.mScrollPort.height ||
-        styles.mVertical != NS_STYLE_OVERFLOW_AUTO) {
+        styles.mVertical != StyleOverflow::Auto) {
       if (mHelper.mHasVerticalScrollbar) {
         // We left room for the vertical scrollbar, but it's not needed;
         // remove it.
@@ -5272,14 +5270,14 @@ nsresult nsXULScrollFrame::XULLayout(nsBoxLayoutState& aState) {
   }
 
   // if scrollbars are auto look at the horizontal case
-  if (styles.mHorizontal != NS_STYLE_OVERFLOW_SCROLL) {
+  if (styles.mHorizontal != StyleOverflow::Scroll) {
     // These are only good until the call to LayoutScrollArea.
     nsRect scrolledRect = mHelper.GetScrolledRect();
 
     // if the child is wider that the scroll area
     // and we don't have a scrollbar add one.
     if ((scrolledRect.width > mHelper.mScrollPort.width) &&
-        styles.mHorizontal == NS_STYLE_OVERFLOW_AUTO) {
+        styles.mHorizontal == StyleOverflow::Auto) {
       if (!mHelper.mHasHorizontalScrollbar) {
         // no scrollbar?
         if (AddHorizontalScrollbar(aState, scrollbarBottom)) {
@@ -5305,7 +5303,7 @@ nsresult nsXULScrollFrame::XULLayout(nsBoxLayoutState& aState) {
           // Refresh scrolledRect because we called LayoutScrollArea.
           scrolledRect = mHelper.GetScrolledRect();
 
-          if (styles.mVertical == NS_STYLE_OVERFLOW_AUTO &&
+          if (styles.mVertical == StyleOverflow::Auto &&
               !mHelper.mHasVerticalScrollbar &&
               scrolledRect.height > mHelper.mScrollPort.height) {
             if (AddVerticalScrollbar(aState, scrollbarRight)) {
@@ -5558,12 +5556,12 @@ bool ScrollFrameHelper::ComputeCustomOverflow(nsOverflowAreas& aOverflowAreas) {
   bool needReflow = false;
   nsPoint scrollPosition = GetScrollPosition();
   if (overflowChange & nsIScrollableFrame::HORIZONTAL) {
-    if (ss.mHorizontal != NS_STYLE_OVERFLOW_HIDDEN || scrollPosition.x) {
+    if (ss.mHorizontal != StyleOverflow::Hidden || scrollPosition.x) {
       needReflow = true;
     }
   }
   if (overflowChange & nsIScrollableFrame::VERTICAL) {
-    if (ss.mVertical != NS_STYLE_OVERFLOW_HIDDEN || scrollPosition.y) {
+    if (ss.mVertical != StyleOverflow::Hidden || scrollPosition.y) {
       needReflow = true;
     }
   }
@@ -6138,7 +6136,7 @@ void ScrollFrameHelper::RestoreState(PresState* aState) {
 
   if (mIsRoot) {
     nsIPresShell* presShell = mOuter->PresShell();
-    presShell->SetResolutionAndScaleTo(aState->resolution(), 
+    presShell->SetResolutionAndScaleTo(aState->resolution(),
                                        nsGkAtoms::restore);
   }
 }
diff --git a/layout/generic/nsGridContainerFrame.cpp b/layout/generic/nsGridContainerFrame.cpp
index 5d18635cb332..2cf3101416ab 100644
--- a/layout/generic/nsGridContainerFrame.cpp
+++ b/layout/generic/nsGridContainerFrame.cpp
@@ -613,7 +613,7 @@ struct nsGridContainerFrame::GridItemInfo {
                   aContainerWM.IsOrthogonalTo(mFrame->GetWritingMode()) &&
               minSize.GetUnit() == eStyleUnit_Enumerated);
     return isAuto &&
-           mFrame->StyleDisplay()->mOverflowX == NS_STYLE_OVERFLOW_VISIBLE;
+           mFrame->StyleDisplay()->mOverflowX == StyleOverflow::Visible;
   }
 
 #ifdef DEBUG
@@ -3597,7 +3597,7 @@ static nscoord MinSize(const GridItemInfo& aGridItem,
                   : style.GetUnit();
   if (unit == eStyleUnit_Enumerated ||
       (unit == eStyleUnit_Auto &&
-       child->StyleDisplay()->mOverflowX == NS_STYLE_OVERFLOW_VISIBLE)) {
+       child->StyleDisplay()->mOverflowX == StyleOverflow::Visible)) {
     // Now calculate the "content size" part and return whichever is smaller.
     MOZ_ASSERT(unit != eStyleUnit_Enumerated || sz == NS_UNCONSTRAINEDSIZE);
     sz = std::min(
diff --git a/layout/generic/nsIScrollableFrame.h b/layout/generic/nsIScrollableFrame.h
index 33361008c68a..2b331d96ec7d 100644
--- a/layout/generic/nsIScrollableFrame.h
+++ b/layout/generic/nsIScrollableFrame.h
@@ -61,8 +61,8 @@ class nsIScrollableFrame : public nsIScrollbarMediator {
   virtual nsIFrame* GetScrolledFrame() const = 0;
 
   /**
-   * Get the styles (NS_STYLE_OVERFLOW_SCROLL, NS_STYLE_OVERFLOW_HIDDEN,
-   * or NS_STYLE_OVERFLOW_AUTO) governing the horizontal and vertical
+   * Get the styles (StyleOverflow::Scroll, StyleOverflow::Hidden,
+   * or StyleOverflow::Auto) governing the horizontal and vertical
    * scrollbars for this frame.
    */
   virtual mozilla::ScrollStyles GetScrollStyles() const = 0;
diff --git a/layout/style/ServoBindings.toml b/layout/style/ServoBindings.toml
index 3ca85bc034ff..0943e5800339 100644
--- a/layout/style/ServoBindings.toml
+++ b/layout/style/ServoBindings.toml
@@ -409,6 +409,7 @@ cbindgen-types = [
     { gecko = "StyleFloat", servo = "values::computed::Float" },
     { gecko = "StyleOverscrollBehavior", servo = "values::computed::OverscrollBehavior" },
     { gecko = "StyleTextAlign", servo = "values::computed::TextAlign" },
+    { gecko = "StyleOverflow", servo = "values::computed::Overflow" },
 ]
 
 mapped-generic-types = [
diff --git a/layout/style/ServoCSSPropList.mako.py b/layout/style/ServoCSSPropList.mako.py
index b10f282cafd9..8e4341dfe211 100644
--- a/layout/style/ServoCSSPropList.mako.py
+++ b/layout/style/ServoCSSPropList.mako.py
@@ -128,6 +128,7 @@ SERIALIZED_PREDEFINED_TYPES = [
     "OverflowClipBox",
     "ScrollSnapType",
     "Float",
+    "Overflow",
 ]
 
 def serialized_by_servo(prop):
diff --git a/layout/style/nsCSSKeywordList.h b/layout/style/nsCSSKeywordList.h
index 23275f34f72b..11e818c1b3db 100644
--- a/layout/style/nsCSSKeywordList.h
+++ b/layout/style/nsCSSKeywordList.h
@@ -48,7 +48,6 @@ CSS_KEY(-moz-grid-group, _moz_grid_group)
 CSS_KEY(-moz-grid-line, _moz_grid_line)
 CSS_KEY(-moz-grid, _moz_grid)
 CSS_KEY(-moz-groupbox, _moz_groupbox)
-CSS_KEY(-moz-hidden-unscrollable, _moz_hidden_unscrollable)
 CSS_KEY(-moz-inline-box, _moz_inline_box)
 CSS_KEY(-moz-inline-grid, _moz_inline_grid)
 CSS_KEY(-moz-inline-stack, _moz_inline_stack)
@@ -116,7 +115,6 @@ CSS_KEY(grabbing, grabbing)
 CSS_KEY(grayscale, grayscale)
 CSS_KEY(grid, grid)
 CSS_KEY(help, help)
-CSS_KEY(hidden, hidden)
 CSS_KEY(hue-rotate, hue_rotate)
 CSS_KEY(infinite, infinite)
 CSS_KEY(inline, inline)
@@ -184,7 +182,6 @@ CSS_KEY(scale3d, scale3d)
 CSS_KEY(scalex, scalex)
 CSS_KEY(scaley, scaley)
 CSS_KEY(scalez, scalez)
-CSS_KEY(scroll, scroll)
 CSS_KEY(se-resize, se_resize)
 CSS_KEY(self-end, self_end)
 CSS_KEY(self-start, self_start)
@@ -230,7 +227,6 @@ CSS_KEY(under, under)
 CSS_KEY(underline, underline)
 CSS_KEY(unsafe, unsafe)
 CSS_KEY(vertical-text, vertical_text)
-CSS_KEY(visible, visible)
 CSS_KEY(w-resize, w_resize)
 CSS_KEY(wait, wait)
 CSS_KEY(wavy, wavy)
diff --git a/layout/style/nsCSSProps.cpp b/layout/style/nsCSSProps.cpp
index efeaaf34416e..8e47f102f234 100644
--- a/layout/style/nsCSSProps.cpp
+++ b/layout/style/nsCSSProps.cpp
@@ -447,15 +447,6 @@ const KTableEntry nsCSSProps::kContainKTable[] = {
     {eCSSKeyword_size, NS_STYLE_CONTAIN_SIZE},
     {eCSSKeyword_UNKNOWN, -1}};
 
-const KTableEntry nsCSSProps::kOverflowSubKTable[] = {
-    {eCSSKeyword_auto, NS_STYLE_OVERFLOW_AUTO},
-    {eCSSKeyword_visible, NS_STYLE_OVERFLOW_VISIBLE},
-    {eCSSKeyword_hidden, NS_STYLE_OVERFLOW_HIDDEN},
-    {eCSSKeyword_scroll, NS_STYLE_OVERFLOW_SCROLL},
-    // Deprecated:
-    {eCSSKeyword__moz_hidden_unscrollable, NS_STYLE_OVERFLOW_CLIP},
-    {eCSSKeyword_UNKNOWN, -1}};
-
 const KTableEntry nsCSSProps::kTextAlignKTable[] = {
     {eCSSKeyword_left, NS_STYLE_TEXT_ALIGN_LEFT},
     {eCSSKeyword_right, NS_STYLE_TEXT_ALIGN_RIGHT},
diff --git a/layout/style/nsCSSProps.h b/layout/style/nsCSSProps.h
index 34eaf36e7883..383c360ffe7d 100644
--- a/layout/style/nsCSSProps.h
+++ b/layout/style/nsCSSProps.h
@@ -316,7 +316,6 @@ class nsCSSProps {
   static const KTableEntry kGridTrackBreadthKTable[];
   static const KTableEntry kLineHeightKTable[];
   static const KTableEntry kContainKTable[];
-  static const KTableEntry kOverflowSubKTable[];
   static const KTableEntry kTextAlignKTable[];
   static const KTableEntry kTextDecorationLineKTable[];
   static const KTableEntry kTextDecorationStyleKTable[];
diff --git a/layout/style/nsComputedDOMStyle.cpp b/layout/style/nsComputedDOMStyle.cpp
index 7b106f2d4d05..6f90b2bff40c 100644
--- a/layout/style/nsComputedDOMStyle.cpp
+++ b/layout/style/nsComputedDOMStyle.cpp
@@ -2515,13 +2515,6 @@ already_AddRefed<CSSValue> nsComputedDOMStyle::DoGetWillChange() {
   return valueList.forget();
 }
 
-already_AddRefed<CSSValue> nsComputedDOMStyle::DoGetOverflowY() {
-  RefPtr<nsROCSSPrimitiveValue> val = new nsROCSSPrimitiveValue;
-  val->SetIdent(nsCSSProps::ValueToKeywordEnum(StyleDisplay()->mOverflowY,
-                                               nsCSSProps::kOverflowSubKTable));
-  return val.forget();
-}
-
 already_AddRefed<CSSValue> nsComputedDOMStyle::DoGetTouchAction() {
   RefPtr<nsROCSSPrimitiveValue> val = new nsROCSSPrimitiveValue;
 
diff --git a/layout/style/nsStyleConsts.h b/layout/style/nsStyleConsts.h
index 743ceb8594cf..198624e827a7 100644
--- a/layout/style/nsStyleConsts.h
+++ b/layout/style/nsStyleConsts.h
@@ -557,15 +557,6 @@ enum class StyleGridTrackBreadth : uint8_t {
 #define NS_STYLE_FRAME_SCROLL 7
 #define NS_STYLE_FRAME_NOSCROLL 8
 
-// See nsStyleDisplay.mOverflow{X,Y}
-#define NS_STYLE_OVERFLOW_VISIBLE 0
-#define NS_STYLE_OVERFLOW_HIDDEN 1
-#define NS_STYLE_OVERFLOW_SCROLL 2
-#define NS_STYLE_OVERFLOW_AUTO 3
-#define NS_STYLE_OVERFLOW_CLIP 4
-#define NS_STYLE_OVERFLOW_SCROLLBARS_HORIZONTAL 5
-#define NS_STYLE_OVERFLOW_SCROLLBARS_VERTICAL 6
-
 // See nsStyleList
 #define NS_STYLE_LIST_STYLE_CUSTOM -1  // for @counter-style
 #define NS_STYLE_LIST_STYLE_NONE 0
diff --git a/layout/style/nsStyleStruct.cpp b/layout/style/nsStyleStruct.cpp
index 46baba45af90..61a456ea2a29 100644
--- a/layout/style/nsStyleStruct.cpp
+++ b/layout/style/nsStyleStruct.cpp
@@ -2977,8 +2977,8 @@ nsStyleDisplay::nsStyleDisplay(const nsPresContext* aContext)
       mBreakInside(StyleBreakWithin::Auto),
       mBreakBefore(StyleBreakBetween::Auto),
       mBreakAfter(StyleBreakBetween::Auto),
-      mOverflowX(NS_STYLE_OVERFLOW_VISIBLE),
-      mOverflowY(NS_STYLE_OVERFLOW_VISIBLE),
+      mOverflowX(StyleOverflow::Visible),
+      mOverflowY(StyleOverflow::Visible),
       mOverflowClipBoxBlock(StyleOverflowClipBox::PaddingBox),
       mOverflowClipBoxInline(StyleOverflowClipBox::PaddingBox),
       mResize(StyleResize::None),
diff --git a/layout/style/nsStyleStruct.h b/layout/style/nsStyleStruct.h
index f616b6f7bfdb..3d2c65369537 100644
--- a/layout/style/nsStyleStruct.h
+++ b/layout/style/nsStyleStruct.h
@@ -1902,8 +1902,8 @@ struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleDisplay {
   mozilla::StyleBreakWithin mBreakInside;
   mozilla::StyleBreakBetween mBreakBefore;
   mozilla::StyleBreakBetween mBreakAfter;
-  uint8_t mOverflowX;  // NS_STYLE_OVERFLOW_*
-  uint8_t mOverflowY;  // NS_STYLE_OVERFLOW_*
+  mozilla::StyleOverflow mOverflowX;
+  mozilla::StyleOverflow mOverflowY;
   mozilla::StyleOverflowClipBox mOverflowClipBoxBlock;
   mozilla::StyleOverflowClipBox mOverflowClipBoxInline;
   mozilla::StyleResize mResize;
@@ -2137,9 +2137,9 @@ struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStyleDisplay {
 
   bool IsScrollableOverflow() const {
     // mOverflowX and mOverflowY always match when one of them is
-    // NS_STYLE_OVERFLOW_VISIBLE or NS_STYLE_OVERFLOW_CLIP.
-    return mOverflowX != NS_STYLE_OVERFLOW_VISIBLE &&
-           mOverflowX != NS_STYLE_OVERFLOW_CLIP;
+    // Visible or MozHiddenUnscrollable.
+    return mOverflowX != mozilla::StyleOverflow::Visible &&
+           mOverflowX != mozilla::StyleOverflow::MozHiddenUnscrollable;
   }
 
   bool IsContainPaint() const {
diff --git a/layout/svg/nsSVGUtils.cpp b/layout/svg/nsSVGUtils.cpp
index dd0eea9f7e12..ff06d754ad51 100644
--- a/layout/svg/nsSVGUtils.cpp
+++ b/layout/svg/nsSVGUtils.cpp
@@ -926,8 +926,8 @@ gfxRect nsSVGUtils::GetClipRectForFrame(nsIFrame* aFrame, float aX, float aY,
     return gfxRect(aX, aY, aWidth, aHeight);
   }
 
-  if (disp->mOverflowX == NS_STYLE_OVERFLOW_HIDDEN ||
-      disp->mOverflowY == NS_STYLE_OVERFLOW_HIDDEN) {
+  if (disp->mOverflowX == StyleOverflow::Hidden ||
+      disp->mOverflowY == StyleOverflow::Hidden) {
     nsIntRect clipPxRect = effects->mClip.ToOutsidePixels(
         aFrame->PresContext()->AppUnitsPerDevPixel());
     gfxRect clipRect = gfxRect(clipPxRect.x, clipPxRect.y, clipPxRect.width,
@@ -940,11 +940,11 @@ gfxRect nsSVGUtils::GetClipRectForFrame(nsIFrame* aFrame, float aX, float aY,
       clipRect.height = aHeight - clipRect.Y();
     }
 
-    if (disp->mOverflowX != NS_STYLE_OVERFLOW_HIDDEN) {
+    if (disp->mOverflowX != StyleOverflow::Hidden) {
       clipRect.x = aX;
       clipRect.width = aWidth;
     }
-    if (disp->mOverflowY != NS_STYLE_OVERFLOW_HIDDEN) {
+    if (disp->mOverflowY != StyleOverflow::Hidden) {
       clipRect.y = aY;
       clipRect.height = aHeight;
     }
diff --git a/layout/xul/nsBox.cpp b/layout/xul/nsBox.cpp
index 7c44da48d2d8..ae834de91d85 100644
--- a/layout/xul/nsBox.cpp
+++ b/layout/xul/nsBox.cpp
@@ -305,10 +305,11 @@ nsresult nsIFrame::XULLayout(nsBoxLayoutState& aState) {
 
 bool nsBox::DoesClipChildren() {
   const nsStyleDisplay* display = StyleDisplay();
-  NS_ASSERTION((display->mOverflowY == NS_STYLE_OVERFLOW_CLIP) ==
-                   (display->mOverflowX == NS_STYLE_OVERFLOW_CLIP),
-               "If one overflow is clip, the other should be too");
-  return display->mOverflowX == NS_STYLE_OVERFLOW_CLIP;
+  NS_ASSERTION(
+      (display->mOverflowY == StyleOverflow::MozHiddenUnscrollable) ==
+          (display->mOverflowX == StyleOverflow::MozHiddenUnscrollable),
+      "If one overflow is -moz-hidden-unscrollable, the other should be too");
+  return display->mOverflowX == StyleOverflow::MozHiddenUnscrollable;
 }
 
 nsresult nsBox::SyncLayout(nsBoxLayoutState& aState) {
diff --git a/servo/components/style/cbindgen.toml b/servo/components/style/cbindgen.toml
index 3b5d56f98826..6005126fb276 100644
--- a/servo/components/style/cbindgen.toml
+++ b/servo/components/style/cbindgen.toml
@@ -64,5 +64,6 @@ include = [
   "ScrollSnapType",
   "OverflowClipBox",
   "Resize",
+  "Overflow",
 ]
 item_types = ["enums", "structs", "typedefs"]
diff --git a/servo/components/style/properties/data.py b/servo/components/style/properties/data.py
index 52d8cf8ec036..8faaa1638230 100644
--- a/servo/components/style/properties/data.py
+++ b/servo/components/style/properties/data.py
@@ -325,6 +325,7 @@ class Longhand(object):
                 "NonNegativeNumber",
                 "Opacity",
                 "OutlineStyle",
+                "Overflow",
                 "OverflowClipBox",
                 "OverflowWrap",
                 "OverscrollBehavior",
diff --git a/servo/components/style/properties/gecko.mako.rs b/servo/components/style/properties/gecko.mako.rs
index 6381bc1f47e2..5f96b42c10a8 100644
--- a/servo/components/style/properties/gecko.mako.rs
+++ b/servo/components/style/properties/gecko.mako.rs
@@ -1394,6 +1394,7 @@ impl Clone for ${style_struct.gecko_struct_name} {
         "OverflowClipBox": impl_simple,
         "ScrollSnapType": impl_simple,
         "Float": impl_simple,
+        "Overflow": impl_simple,
         "BreakBetween": impl_simple,
         "BreakWithin": impl_simple,
         "Resize": impl_simple,
@@ -3011,7 +3012,7 @@ fn static_assert() {
     }
 </%def>
 
-<% skip_box_longhands= """display overflow-y vertical-align
+<% skip_box_longhands= """display vertical-align
                           animation-name animation-delay animation-duration
                           animation-direction animation-fill-mode animation-play-state
                           animation-iteration-count animation-timing-function
@@ -3063,28 +3064,6 @@ fn static_assert() {
     ) %>
     ${impl_keyword('clear', 'mBreakType', clear_keyword)}
 
-    <% overflow_x = data.longhands_by_name["overflow-x"] %>
-    pub fn set_overflow_y(&mut self, v: longhands::overflow_y::computed_value::T) {
-        use crate::properties::longhands::overflow_x::computed_value::T as BaseType;
-        // FIXME(bholley): Align binary representations and ditch |match| for cast + static_asserts
-        self.gecko.mOverflowY = match v {
-            % for value in overflow_x.keyword.values_for('gecko'):
-                BaseType::${to_camel_case(value)} => structs::${overflow_x.keyword.gecko_constant(value)} as u8,
-            % endfor
-        };
-    }
-    ${impl_simple_copy('overflow_y', 'mOverflowY')}
-    pub fn clone_overflow_y(&self) -> longhands::overflow_y::computed_value::T {
-        use crate::properties::longhands::overflow_x::computed_value::T as BaseType;
-        // FIXME(bholley): Align binary representations and ditch |match| for cast + static_asserts
-        match self.gecko.mOverflowY as u32 {
-            % for value in overflow_x.keyword.values_for('gecko'):
-            structs::${overflow_x.keyword.gecko_constant(value)} => BaseType::${to_camel_case(value)},
-            % endfor
-            x => panic!("Found unexpected value in style struct for overflow_y property: {}", x),
-        }
-    }
-
     pub fn set_vertical_align(&mut self, v: longhands::vertical_align::computed_value::T) {
         use crate::values::generics::box_::VerticalAlign;
         let value = match v {
diff --git a/servo/components/style/properties/longhands/box.mako.rs b/servo/components/style/properties/longhands/box.mako.rs
index f0bf6b0bcdb7..1e0629861e45 100644
--- a/servo/components/style/properties/longhands/box.mako.rs
+++ b/servo/components/style/properties/longhands/box.mako.rs
@@ -100,34 +100,30 @@ ${helpers.single_keyword("-servo-overflow-clip-box", "padding-box content-box",
     )}
 % endfor
 
-<%
-    overflow_custom_consts = { "-moz-hidden-unscrollable": "CLIP" }
-%>
-
 // FIXME(pcwalton, #2742): Implement scrolling for `scroll` and `auto`.
 //
 // We allow it to apply to placeholders for UA sheets, which set it !important.
-${helpers.single_keyword(
+${helpers.predefined_type(
     "overflow-x",
-    "visible hidden scroll auto",
+    "Overflow",
+    "computed::Overflow::Visible",
     animation_value_type="discrete",
-    extra_gecko_values="-moz-hidden-unscrollable",
-    custom_consts=overflow_custom_consts,
-    gecko_constant_prefix="NS_STYLE_OVERFLOW",
     flags="APPLIES_TO_PLACEHOLDER",
     spec="https://drafts.csswg.org/css-overflow/#propdef-overflow-x",
+    needs_context=False,
     servo_restyle_damage = "reflow",
 )}
 
-// FIXME(pcwalton, #2742): Implement scrolling for `scroll` and `auto`.
-//
-// We allow it to apply to placeholders for UA sheets, which set it !important.
-<%helpers:longhand name="overflow-y" animation_value_type="discrete"
-                   flags="APPLIES_TO_PLACEHOLDER",
-                   spec="https://drafts.csswg.org/css-overflow/#propdef-overflow-y"
-                   servo_restyle_damage = "reflow">
-    pub use super::overflow_x::{SpecifiedValue, parse, get_initial_value, computed_value};
-</%helpers:longhand>
+${helpers.predefined_type(
+    "overflow-y",
+    "Overflow",
+    "computed::Overflow::Visible",
+    animation_value_type="discrete",
+    flags="APPLIES_TO_PLACEHOLDER",
+    spec="https://drafts.csswg.org/css-overflow/#propdef-overflow-y",
+    needs_context=False,
+    servo_restyle_damage = "reflow",
+)}
 
 <% transition_extra_prefixes = "moz:layout.css.prefixes.transitions webkit" %>
 
diff --git a/servo/components/style/values/computed/box.rs b/servo/components/style/values/computed/box.rs
index 9ba38f040155..32ac16fb5749 100644
--- a/servo/components/style/values/computed/box.rs
+++ b/servo/components/style/values/computed/box.rs
@@ -13,7 +13,7 @@ use crate::values::specified::box_ as specified;
 
 pub use crate::values::specified::box_::{AnimationName, Appearance, BreakBetween, BreakWithin};
 pub use crate::values::specified::box_::{Clear as SpecifiedClear, Float as SpecifiedFloat};
-pub use crate::values::specified::box_::{Contain, Display, OverflowClipBox};
+pub use crate::values::specified::box_::{Contain, Display, Overflow, OverflowClipBox};
 pub use crate::values::specified::box_::{OverscrollBehavior, ScrollSnapType};
 pub use crate::values::specified::box_::{TouchAction, TransitionProperty, WillChange};
 
diff --git a/servo/components/style/values/computed/mod.rs b/servo/components/style/values/computed/mod.rs
index d05d42e01022..8e135b52caa4 100644
--- a/servo/components/style/values/computed/mod.rs
+++ b/servo/components/style/values/computed/mod.rs
@@ -43,7 +43,7 @@ pub use self::border::{BorderImageRepeat, BorderImageSideWidth};
 pub use self::border::{BorderImageSlice, BorderImageWidth};
 pub use self::box_::{AnimationIterationCount, AnimationName, Contain};
 pub use self::box_::{Appearance, BreakBetween, BreakWithin, Clear, Float};
-pub use self::box_::{Display, TransitionProperty};
+pub use self::box_::{Display, TransitionProperty, Overflow};
 pub use self::box_::{OverflowClipBox, OverscrollBehavior, Perspective, Resize};
 pub use self::box_::{ScrollSnapType, TouchAction, VerticalAlign, WillChange};
 pub use self::color::{Color, ColorPropertyValue, RGBAColor};
diff --git a/servo/components/style/values/specified/box.rs b/servo/components/style/values/specified/box.rs
index 84cbe9e879c2..54030ba71395 100644
--- a/servo/components/style/values/specified/box.rs
+++ b/servo/components/style/values/specified/box.rs
@@ -1363,3 +1363,28 @@ pub enum BreakWithin {
     Auto,
     Avoid,
 }
+
+/// The value for the `overflow-x` / `overflow-y` properties.
+#[allow(missing_docs)]
+#[derive(
+    Clone,
+    Copy,
+    Debug,
+    Eq,
+    Hash,
+    MallocSizeOf,
+    Parse,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToCss,
+    ToComputedValue,
+)]
+#[repr(u8)]
+pub enum Overflow {
+    Visible,
+    Hidden,
+    Scroll,
+    Auto,
+    #[cfg(feature = "gecko")]
+    MozHiddenUnscrollable,
+}
diff --git a/servo/components/style/values/specified/mod.rs b/servo/components/style/values/specified/mod.rs
index c185dce80d05..3b8278c3287e 100644
--- a/servo/components/style/values/specified/mod.rs
+++ b/servo/components/style/values/specified/mod.rs
@@ -36,7 +36,7 @@ pub use self::border::{BorderCornerRadius, BorderImageSlice, BorderImageWidth};
 pub use self::border::{BorderImageRepeat, BorderImageSideWidth};
 pub use self::border::{BorderRadius, BorderSideWidth, BorderSpacing, BorderStyle};
 pub use self::box_::{AnimationIterationCount, AnimationName, Contain, Display};
-pub use self::box_::{Appearance, BreakBetween, BreakWithin, Clear, Float};
+pub use self::box_::{Appearance, BreakBetween, BreakWithin, Clear, Float, Overflow};
 pub use self::box_::{OverflowClipBox, OverscrollBehavior, Perspective, Resize};
 pub use self::box_::{ScrollSnapType, TouchAction, TransitionProperty, VerticalAlign, WillChange};
 pub use self::color::{Color, ColorPropertyValue, RGBAColor};