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diff --git a/gfx/2d/RectAbsolute.h b/gfx/2d/RectAbsolute.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef MOZILLA_GFX_RECT_ABSOLUTE_H_
+#define MOZILLA_GFX_RECT_ABSOLUTE_H_
+
+#include <algorithm>
+#include <cstdint>
+
+#include "mozilla/Attributes.h"
+#include "Point.h"
+#include "Rect.h"
+#include "Types.h"
+
+namespace mozilla {
+
+template <typename>
+struct IsPixel;
+
+namespace gfx {
+
+/**
+ * A RectAbsolute is similar to a Rect (see BaseRect.h), but represented as
+ * (x1, y1, x2, y2) instead of (x, y, width, height).
+ *
+ * Unless otherwise indicated, methods on this class correspond
+ * to methods on BaseRect.
+ *
+ * The API is currently very bare-bones; it may be extended as needed.
+ *
+ * Do not use this class directly. Subclass it, pass that subclass as the
+ * Sub parameter, and only use that subclass.
+ */
+template <class T, class Sub, class Point, class Rect>
+struct BaseRectAbsolute {
+ protected:
+  T left, top, right, bottom;
+
+ public:
+  BaseRectAbsolute() : left(0), top(0), right(0), bottom(0) {}
+  BaseRectAbsolute(T aLeft, T aTop, T aRight, T aBottom)
+      : left(aLeft), top(aTop), right(aRight), bottom(aBottom) {}
+
+  MOZ_ALWAYS_INLINE T X() const { return left; }
+  MOZ_ALWAYS_INLINE T Y() const { return top; }
+  MOZ_ALWAYS_INLINE T Width() const { return right - left; }
+  MOZ_ALWAYS_INLINE T Height() const { return bottom - top; }
+  MOZ_ALWAYS_INLINE T XMost() const { return right; }
+  MOZ_ALWAYS_INLINE T YMost() const { return bottom; }
+  MOZ_ALWAYS_INLINE const T& Left() const { return left; }
+  MOZ_ALWAYS_INLINE const T& Right() const { return right; }
+  MOZ_ALWAYS_INLINE const T& Top() const { return top; }
+  MOZ_ALWAYS_INLINE const T& Bottom() const { return bottom; }
+  MOZ_ALWAYS_INLINE T& Left() { return left; }
+  MOZ_ALWAYS_INLINE T& Right() { return right; }
+  MOZ_ALWAYS_INLINE T& Top() { return top; }
+  MOZ_ALWAYS_INLINE T& Bottom() { return bottom; }
+  T Area() const { return Width() * Height(); }
+
+  void Inflate(T aD) { Inflate(aD, aD); }
+  void Inflate(T aDx, T aDy) {
+    left -= aDx;
+    top -= aDy;
+    right += aDx;
+    bottom += aDy;
+  }
+
+  MOZ_ALWAYS_INLINE void SetBox(T aLeft, T aTop, T aRight, T aBottom) {
+    left = aLeft;
+    top = aTop;
+    right = aRight;
+    bottom = aBottom;
+  }
+  void SetLeftEdge(T aLeft) { left = aLeft; }
+  void SetRightEdge(T aRight) { right = aRight; }
+  void SetTopEdge(T aTop) { top = aTop; }
+  void SetBottomEdge(T aBottom) { bottom = aBottom; }
+
+  static Sub FromRect(const Rect& aRect) {
+    if (aRect.Overflows()) {
+      return Sub();
+    }
+    return Sub(aRect.x, aRect.y, aRect.XMost(), aRect.YMost());
+  }
+
+  [[nodiscard]] Sub Intersect(const Sub& aOther) const {
+    Sub result;
+    result.left = std::max<T>(left, aOther.left);
+    result.top = std::max<T>(top, aOther.top);
+    result.right = std::min<T>(right, aOther.right);
+    result.bottom = std::min<T>(bottom, aOther.bottom);
+    if (result.right < result.left || result.bottom < result.top) {
+      result.SizeTo(0, 0);
+    }
+    return result;
+  }
+
+  bool IsEmpty() const { return right <= left || bottom <= top; }
+
+  bool IsEqualEdges(const Sub& aOther) const {
+    return left == aOther.left && top == aOther.top && right == aOther.right &&
+           bottom == aOther.bottom;
+  }
+
+  bool IsEqualInterior(const Sub& aRect) const {
+    return IsEqualEdges(aRect) || (IsEmpty() && aRect.IsEmpty());
+  }
+
+  MOZ_ALWAYS_INLINE void MoveBy(T aDx, T aDy) {
+    left += aDx;
+    right += aDx;
+    top += aDy;
+    bottom += aDy;
+  }
+  MOZ_ALWAYS_INLINE void MoveBy(const Point& aPoint) {
+    left += aPoint.x;
+    right += aPoint.x;
+    top += aPoint.y;
+    bottom += aPoint.y;
+  }
+  MOZ_ALWAYS_INLINE void SizeTo(T aWidth, T aHeight) {
+    right = left + aWidth;
+    bottom = top + aHeight;
+  }
+
+  bool Contains(const Sub& aRect) const {
+    return aRect.IsEmpty() || (left <= aRect.left && aRect.right <= right &&
+                               top <= aRect.top && aRect.bottom <= bottom);
+  }
+  bool Contains(T aX, T aY) const {
+    return (left <= aX && aX < right && top <= aY && aY < bottom);
+  }
+
+  bool Intersects(const Sub& aRect) const {
+    return !IsEmpty() && !aRect.IsEmpty() && left < aRect.right &&
+           aRect.left < right && top < aRect.bottom && aRect.top < bottom;
+  }
+
+  void SetEmpty() { left = right = top = bottom = 0; }
+
+  // Returns the smallest rectangle that contains both the area of both
+  // this and aRect2.
+  // Thus, empty input rectangles are ignored.
+  // If both rectangles are empty, returns this.
+  // WARNING! This is not safe against overflow, prefer using SafeUnion instead
+  // when dealing with int-based rects.
+  [[nodiscard]] Sub Union(const Sub& aRect) const {
+    if (IsEmpty()) {
+      return aRect;
+    } else if (aRect.IsEmpty()) {
+      return *static_cast<const Sub*>(this);
+    } else {
+      return UnionEdges(aRect);
+    }
+  }
+  // Returns the smallest rectangle that contains both the points (including
+  // edges) of both aRect1 and aRect2.
+  // Thus, empty input rectangles are allowed to affect the result.
+  // WARNING! This is not safe against overflow, prefer using SafeUnionEdges
+  // instead when dealing with int-based rects.
+  [[nodiscard]] Sub UnionEdges(const Sub& aRect) const {
+    Sub result;
+    result.left = std::min(left, aRect.left);
+    result.top = std::min(top, aRect.top);
+    result.right = std::max(XMost(), aRect.XMost());
+    result.bottom = std::max(YMost(), aRect.YMost());
+    return result;
+  }
+
+  // Scale 'this' by aScale without doing any rounding.
+  void Scale(T aScale) { Scale(aScale, aScale); }
+  // Scale 'this' by aXScale and aYScale, without doing any rounding.
+  void Scale(T aXScale, T aYScale) {
+    right = XMost() * aXScale;
+    bottom = YMost() * aYScale;
+    left = left * aXScale;
+    top = top * aYScale;
+  }
+  // Scale 'this' by aScale, converting coordinates to integers so that the
+  // result is the smallest integer-coordinate rectangle containing the
+  // unrounded result. Note: this can turn an empty rectangle into a non-empty
+  // rectangle
+  void ScaleRoundOut(double aScale) { ScaleRoundOut(aScale, aScale); }
+  // Scale 'this' by aXScale and aYScale, converting coordinates to integers so
+  // that the result is the smallest integer-coordinate rectangle containing the
+  // unrounded result.
+  // Note: this can turn an empty rectangle into a non-empty rectangle
+  void ScaleRoundOut(double aXScale, double aYScale) {
+    right = static_cast<T>(ceil(double(XMost()) * aXScale));
+    bottom = static_cast<T>(ceil(double(YMost()) * aYScale));
+    left = static_cast<T>(floor(double(left) * aXScale));
+    top = static_cast<T>(floor(double(top) * aYScale));
+  }
+  // Scale 'this' by aScale, converting coordinates to integers so that the
+  // result is the largest integer-coordinate rectangle contained by the
+  // unrounded result.
+  void ScaleRoundIn(double aScale) { ScaleRoundIn(aScale, aScale); }
+  // Scale 'this' by aXScale and aYScale, converting coordinates to integers so
+  // that the result is the largest integer-coordinate rectangle contained by
+  // the unrounded result.
+  void ScaleRoundIn(double aXScale, double aYScale) {
+    right = static_cast<T>(floor(double(XMost()) * aXScale));
+    bottom = static_cast<T>(floor(double(YMost()) * aYScale));
+    left = static_cast<T>(ceil(double(left) * aXScale));
+    top = static_cast<T>(ceil(double(top) * aYScale));
+  }
+  // Scale 'this' by 1/aScale, converting coordinates to integers so that the
+  // result is the smallest integer-coordinate rectangle containing the
+  // unrounded result. Note: this can turn an empty rectangle into a non-empty
+  // rectangle
+  void ScaleInverseRoundOut(double aScale) {
+    ScaleInverseRoundOut(aScale, aScale);
+  }
+  // Scale 'this' by 1/aXScale and 1/aYScale, converting coordinates to integers
+  // so that the result is the smallest integer-coordinate rectangle containing
+  // the unrounded result. Note: this can turn an empty rectangle into a
+  // non-empty rectangle
+  void ScaleInverseRoundOut(double aXScale, double aYScale) {
+    right = static_cast<T>(ceil(double(XMost()) / aXScale));
+    bottom = static_cast<T>(ceil(double(YMost()) / aYScale));
+    left = static_cast<T>(floor(double(left) / aXScale));
+    top = static_cast<T>(floor(double(top) / aYScale));
+  }
+  // Scale 'this' by 1/aScale, converting coordinates to integers so that the
+  // result is the largest integer-coordinate rectangle contained by the
+  // unrounded result.
+  void ScaleInverseRoundIn(double aScale) {
+    ScaleInverseRoundIn(aScale, aScale);
+  }
+  // Scale 'this' by 1/aXScale and 1/aYScale, converting coordinates to integers
+  // so that the result is the largest integer-coordinate rectangle contained by
+  // the unrounded result.
+  void ScaleInverseRoundIn(double aXScale, double aYScale) {
+    right = static_cast<T>(floor(double(XMost()) / aXScale));
+    bottom = static_cast<T>(floor(double(YMost()) / aYScale));
+    left = static_cast<T>(ceil(double(left) / aXScale));
+    top = static_cast<T>(ceil(double(top) / aYScale));
+  }
+
+  /**
+   * Translate this rectangle to be inside aRect. If it doesn't fit inside
+   * aRect then the dimensions that don't fit will be shrunk so that they
+   * do fit. The resulting rect is returned.
+   */
+  [[nodiscard]] Sub MoveInsideAndClamp(const Sub& aRect) const {
+    T newLeft = std::max(aRect.left, left);
+    T newTop = std::max(aRect.top, top);
+    T width = std::min(aRect.Width(), Width());
+    T height = std::min(aRect.Height(), Height());
+    Sub rect(newLeft, newTop, newLeft + width, newTop + height);
+    newLeft = std::min(rect.right, aRect.right) - width;
+    newTop = std::min(rect.bottom, aRect.bottom) - height;
+    rect.MoveBy(newLeft - rect.left, newTop - rect.top);
+    return rect;
+  }
+
+  friend std::ostream& operator<<(
+      std::ostream& stream,
+      const BaseRectAbsolute<T, Sub, Point, Rect>& aRect) {
+    return stream << "(l=" << aRect.left << ", t=" << aRect.top
+                  << ", r=" << aRect.right << ", b=" << aRect.bottom << ')';
+  }
+};
+
+template <class Units>
+struct IntRectAbsoluteTyped
+    : public BaseRectAbsolute<int32_t, IntRectAbsoluteTyped<Units>,
+                              IntPointTyped<Units>, IntRectTyped<Units>>,
+      public Units {
+  static_assert(IsPixel<Units>::value,
+                "'units' must be a coordinate system tag");
+  typedef BaseRectAbsolute<int32_t, IntRectAbsoluteTyped<Units>,
+                           IntPointTyped<Units>, IntRectTyped<Units>>
+      Super;
+  typedef IntParam<int32_t> ToInt;
+
+  IntRectAbsoluteTyped() : Super() {}
+  IntRectAbsoluteTyped(ToInt aLeft, ToInt aTop, ToInt aRight, ToInt aBottom)
+      : Super(aLeft.value, aTop.value, aRight.value, aBottom.value) {}
+};
+
+template <class Units>
+struct RectAbsoluteTyped
+    : public BaseRectAbsolute<Float, RectAbsoluteTyped<Units>,
+                              PointTyped<Units>, RectTyped<Units>>,
+      public Units {
+  static_assert(IsPixel<Units>::value,
+                "'units' must be a coordinate system tag");
+  typedef BaseRectAbsolute<Float, RectAbsoluteTyped<Units>, PointTyped<Units>,
+                           RectTyped<Units>>
+      Super;
+
+  RectAbsoluteTyped() : Super() {}
+  RectAbsoluteTyped(Float aLeft, Float aTop, Float aRight, Float aBottom)
+      : Super(aLeft, aTop, aRight, aBottom) {}
+};
+
+typedef IntRectAbsoluteTyped<UnknownUnits> IntRectAbsolute;
+
+}  // namespace gfx
+}  // namespace mozilla
+
+#endif /* MOZILLA_GFX_RECT_ABSOLUTE_H_ */