--- a/layout/style/nsCSSKeywordList.h
+++ b/layout/style/nsCSSKeywordList.h
@@ -306,16 +306,17 @@ CSS_KEY(inline, inline)
 CSS_KEY(inline-axis, inline_axis)
 CSS_KEY(inline-block, inline_block)
 CSS_KEY(inline-flex, inline_flex)
 CSS_KEY(inline-grid, inline_grid)
 CSS_KEY(inline-table, inline_table)
 CSS_KEY(inset, inset)
 CSS_KEY(inside, inside)
 CSS_KEY(interpolatematrix, interpolatematrix)
+CSS_KEY(isolate, isolate)
 CSS_KEY(invert, invert)
 CSS_KEY(italic, italic)
 CSS_KEY(japanese-formal, japanese_formal)
 CSS_KEY(japanese-informal, japanese_informal)
 CSS_KEY(jis78, jis78)
 CSS_KEY(jis83, jis83)
 CSS_KEY(jis90, jis90)
 CSS_KEY(jis04, jis04)

--- a/layout/style/nsCSSPropList.h
+++ b/layout/style/nsCSSPropList.h
@@ -2516,16 +2516,27 @@ CSS_PROP_DISPLAY(
     MixBlendMode,
     CSS_PROPERTY_PARSE_VALUE |
         CSS_PROPERTY_CREATES_STACKING_CONTEXT,
     "layout.css.mix-blend-mode.enabled",
     VARIANT_HK,
     kBlendModeKTable,
     CSS_PROP_NO_OFFSET,
     eStyleAnimType_None)
+CSS_PROP_DISPLAY(
+    isolation,
+    isolation,
+    Isolation,
+    CSS_PROPERTY_PARSE_VALUE |
+        CSS_PROPERTY_CREATES_STACKING_CONTEXT,
+    "layout.css.isolation.enabled",
+    VARIANT_HK,
+    kIsolationKTable,
+    CSS_PROP_NO_OFFSET,
+    eStyleAnimType_None)
 CSS_PROP_POSITION(
     object-fit,
     object_fit,
     ObjectFit,
     CSS_PROPERTY_PARSE_VALUE,
     "layout.css.object-fit-and-position.enabled",
     VARIANT_HK,
     kObjectFitKTable,

--- a/layout/style/nsCSSProps.cpp
+++ b/layout/style/nsCSSProps.cpp
@@ -1342,16 +1342,22 @@ const KTableValue nsCSSProps::kImageOrie
   eCSSKeyword_UNKNOWN,-1
 };
 
 const KTableValue nsCSSProps::kImageOrientationFlipKTable[] = {
   eCSSKeyword_flip, NS_STYLE_IMAGE_ORIENTATION_FLIP,
   eCSSKeyword_UNKNOWN,-1
 };
 
+const KTableValue nsCSSProps::kIsolationKTable[] = {
+  eCSSKeyword_auto, NS_STYLE_ISOLATION_AUTO,
+  eCSSKeyword_isolate, NS_STYLE_ISOLATION_ISOLATE,
+  eCSSKeyword_UNKNOWN,-1
+};
+
 const KTableValue nsCSSProps::kIMEModeKTable[] = {
   eCSSKeyword_normal, NS_STYLE_IME_MODE_NORMAL,
   eCSSKeyword_auto, NS_STYLE_IME_MODE_AUTO,
   eCSSKeyword_active, NS_STYLE_IME_MODE_ACTIVE,
   eCSSKeyword_disabled, NS_STYLE_IME_MODE_DISABLED,
   eCSSKeyword_inactive, NS_STYLE_IME_MODE_INACTIVE,
   eCSSKeyword_UNKNOWN,-1
 };

--- a/layout/style/nsCSSProps.h
+++ b/layout/style/nsCSSProps.h
@@ -589,16 +589,17 @@ public:
   static const KTableValue kFontVariantLigaturesKTable[];
   static const KTableValue kFontVariantNumericKTable[];
   static const KTableValue kFontVariantPositionKTable[];
   static const KTableValue kFontWeightKTable[];
   static const KTableValue kGridAutoFlowKTable[];
   static const KTableValue kGridTrackBreadthKTable[];
   static const KTableValue kImageOrientationKTable[];
   static const KTableValue kImageOrientationFlipKTable[];
+  static const KTableValue kIsolationKTable[];
   static const KTableValue kIMEModeKTable[];
   static const KTableValue kLineHeightKTable[];
   static const KTableValue kListStylePositionKTable[];
   static const KTableValue kListStyleKTable[];
   static const KTableValue kMaskTypeKTable[];
   static const KTableValue kMathVariantKTable[];
   static const KTableValue kMathDisplayKTable[];
   static const KTableValue kContextOpacityKTable[];

--- a/layout/style/nsComputedDOMStyle.cpp
+++ b/layout/style/nsComputedDOMStyle.cpp
@@ -4224,16 +4224,25 @@ nsComputedDOMStyle::DoGetMixBlendMode()
 {
   nsROCSSPrimitiveValue* val = new nsROCSSPrimitiveValue;
   val->SetIdent(nsCSSProps::ValueToKeywordEnum(StyleDisplay()->mMixBlendMode,
                                                nsCSSProps::kBlendModeKTable));
   return val;
 }
 
 CSSValue*
+nsComputedDOMStyle::DoGetIsolation()
+{
+  nsROCSSPrimitiveValue* val = new nsROCSSPrimitiveValue;
+  val->SetIdent(nsCSSProps::ValueToKeywordEnum(StyleDisplay()->mIsolation,
+                                               nsCSSProps::kIsolationKTable));
+  return val;
+}
+
+CSSValue*
 nsComputedDOMStyle::DoGetObjectFit()
 {
   nsROCSSPrimitiveValue* val = new nsROCSSPrimitiveValue;
   val->SetIdent(nsCSSProps::ValueToKeywordEnum(StylePosition()->mObjectFit,
                                                nsCSSProps::kObjectFitKTable));
   return val;
 }
 

--- a/layout/style/nsComputedDOMStyle.h
+++ b/layout/style/nsComputedDOMStyle.h
@@ -230,16 +230,17 @@ private:
 
   mozilla::dom::CSSValue* DoGetWidth();
   mozilla::dom::CSSValue* DoGetHeight();
   mozilla::dom::CSSValue* DoGetMaxHeight();
   mozilla::dom::CSSValue* DoGetMaxWidth();
   mozilla::dom::CSSValue* DoGetMinHeight();
   mozilla::dom::CSSValue* DoGetMinWidth();
   mozilla::dom::CSSValue* DoGetMixBlendMode();
+  mozilla::dom::CSSValue* DoGetIsolation();
   mozilla::dom::CSSValue* DoGetObjectFit();
   mozilla::dom::CSSValue* DoGetObjectPosition();
   mozilla::dom::CSSValue* DoGetLeft();
   mozilla::dom::CSSValue* DoGetTop();
   mozilla::dom::CSSValue* DoGetRight();
   mozilla::dom::CSSValue* DoGetBottom();
   mozilla::dom::CSSValue* DoGetStackSizing();
 

--- a/layout/style/nsComputedDOMStylePropertyList.h
+++ b/layout/style/nsComputedDOMStylePropertyList.h
@@ -141,16 +141,17 @@ COMPUTED_STYLE_PROP(grid_column_start,  
 COMPUTED_STYLE_PROP(grid_row_end,                  GridRowEnd)
 COMPUTED_STYLE_PROP(grid_row_start,                GridRowStart)
 COMPUTED_STYLE_PROP(grid_template_areas,           GridTemplateAreas)
 COMPUTED_STYLE_PROP(grid_template_columns,         GridTemplateColumns)
 COMPUTED_STYLE_PROP(grid_template_rows,            GridTemplateRows)
 COMPUTED_STYLE_PROP(height,                        Height)
 COMPUTED_STYLE_PROP(image_orientation,             ImageOrientation)
 COMPUTED_STYLE_PROP(ime_mode,                      IMEMode)
+COMPUTED_STYLE_PROP(isolation,                     Isolation)
 COMPUTED_STYLE_PROP(justify_content,               JustifyContent)
 COMPUTED_STYLE_PROP(left,                          Left)
 COMPUTED_STYLE_PROP(letter_spacing,                LetterSpacing)
 COMPUTED_STYLE_PROP(line_height,                   LineHeight)
 //// COMPUTED_STYLE_PROP(list_style,               ListStyle)
 COMPUTED_STYLE_PROP(list_style_image,              ListStyleImage)
 COMPUTED_STYLE_PROP(list_style_position,           ListStylePosition)
 COMPUTED_STYLE_PROP(list_style_type,               ListStyleType)

--- a/layout/style/nsRuleNode.cpp
+++ b/layout/style/nsRuleNode.cpp
@@ -5292,16 +5292,23 @@ nsRuleNode::ComputeDisplayData(void* aSt
 
   // mix-blend-mode: enum, inherit, initial
   SetDiscrete(*aRuleData->ValueForMixBlendMode(), display->mMixBlendMode,
               canStoreInRuleTree,
               SETDSC_ENUMERATED | SETDSC_UNSET_INITIAL,
               parentDisplay->mMixBlendMode, NS_STYLE_BLEND_NORMAL,
               0, 0, 0, 0);
 
+    // isolation: enum, inherit, initial
+  SetDiscrete(*aRuleData->ValueForIsolation(), display->mIsolation,
+              canStoreInRuleTree,
+              SETDSC_ENUMERATED | SETDSC_UNSET_INITIAL,
+              parentDisplay->mIsolation, NS_STYLE_ISOLATION_AUTO,
+              0, 0, 0, 0);
+
   // Backup original display value for calculation of a hypothetical
   // box (CSS2 10.6.4/10.6.5), in addition to getting our style data right later.
   // See nsHTMLReflowState::CalculateHypotheticalBox
   display->mOriginalDisplay = display->mDisplay;
 
   // appearance: enum, inherit, initial
   SetDiscrete(*aRuleData->ValueForAppearance(),
               display->mAppearance, canStoreInRuleTree,

--- a/layout/style/nsStyleConsts.h
+++ b/layout/style/nsStyleConsts.h
@@ -715,16 +715,20 @@ static inline mozilla::css::Side operato
 #define NS_STYLE_POINTER_EVENTS_STROKE          7
 #define NS_STYLE_POINTER_EVENTS_ALL             8
 #define NS_STYLE_POINTER_EVENTS_AUTO            9
 
 // See nsStyleVisibility.mImageOrientationType
 #define NS_STYLE_IMAGE_ORIENTATION_FLIP         0
 #define NS_STYLE_IMAGE_ORIENTATION_FROM_IMAGE   1
 
+// See nsStyleDisplay
+#define NS_STYLE_ISOLATION_AUTO                 0
+#define NS_STYLE_ISOLATION_ISOLATE              1
+
 // See nsStylePosition.mObjectFit
 #define NS_STYLE_OBJECT_FIT_FILL                0
 #define NS_STYLE_OBJECT_FIT_CONTAIN             1
 #define NS_STYLE_OBJECT_FIT_COVER               2
 #define NS_STYLE_OBJECT_FIT_NONE                3
 #define NS_STYLE_OBJECT_FIT_SCALE_DOWN          4
 
 // See nsStyleDisplay

--- a/layout/style/nsStyleStruct.cpp
+++ b/layout/style/nsStyleStruct.cpp
@@ -2577,16 +2577,17 @@ nsStyleDisplay::nsStyleDisplay()
   mTransformOrigin[2].SetCoordValue(0);
   mPerspectiveOrigin[0].SetPercentValue(0.5f);
   mPerspectiveOrigin[1].SetPercentValue(0.5f);
   mChildPerspective.SetNoneValue();
   mBackfaceVisibility = NS_STYLE_BACKFACE_VISIBILITY_VISIBLE;
   mTransformStyle = NS_STYLE_TRANSFORM_STYLE_FLAT;
   mOrient = NS_STYLE_ORIENT_AUTO;
   mMixBlendMode = NS_STYLE_BLEND_NORMAL;
+  mIsolation = NS_STYLE_ISOLATION_AUTO;
   mTouchAction = NS_STYLE_TOUCH_ACTION_AUTO;
 
   mTransitions.AppendElement();
   NS_ABORT_IF_FALSE(mTransitions.Length() == 1,
                     "appending within auto buffer should never fail");
   mTransitions[0].SetInitialValues();
   mTransitionTimingFunctionCount = 1;
   mTransitionDurationCount = 1;
@@ -2623,16 +2624,17 @@ nsStyleDisplay::nsStyleDisplay(const nsS
   , mBreakAfter(aSource.mBreakAfter)
   , mOverflowX(aSource.mOverflowX)
   , mOverflowY(aSource.mOverflowY)
   , mOverflowClipBox(aSource.mOverflowClipBox)
   , mResize(aSource.mResize)
   , mClipFlags(aSource.mClipFlags)
   , mOrient(aSource.mOrient)
   , mMixBlendMode(aSource.mMixBlendMode)
+  , mIsolation(aSource.mIsolation)
   , mWillChangeBitField(aSource.mWillChangeBitField)
   , mWillChange(aSource.mWillChange)
   , mTouchAction(aSource.mTouchAction)
   , mBackfaceVisibility(aSource.mBackfaceVisibility)
   , mTransformStyle(aSource.mTransformStyle)
   , mSpecifiedTransform(aSource.mSpecifiedTransform)
   , mChildPerspective(aSource.mChildPerspective)
   , mTransitions(aSource.mTransitions)
@@ -2721,17 +2723,18 @@ nsChangeHint nsStyleDisplay::CalcDiffere
     if ((mOpacity >= 0.99f && mOpacity < 1.0f && aOther.mOpacity == 1.0f) ||
         (aOther.mOpacity >= 0.99f && aOther.mOpacity < 1.0f && mOpacity == 1.0f)) {
       NS_UpdateHint(hint, nsChangeHint_RepaintFrame);
     } else {
       NS_UpdateHint(hint, nsChangeHint_UpdateOpacityLayer);
     }
   }
 
-  if (mMixBlendMode != aOther.mMixBlendMode) {
+  if (mMixBlendMode != aOther.mMixBlendMode
+      || mIsolation != aOther.mIsolation) {
     NS_UpdateHint(hint, nsChangeHint_RepaintFrame);
   }
 
   /* If we've added or removed the transform property, we need to reconstruct the frame to add
    * or remove the view object, and also to handle abs-pos and fixed-pos containers.
    */
   if (HasTransformStyle() != aOther.HasTransformStyle()) {
     // We do not need to apply nsChangeHint_UpdateTransformLayer since

--- a/layout/style/nsStyleStruct.h
+++ b/layout/style/nsStyleStruct.h
@@ -2018,16 +2018,17 @@ struct nsStyleDisplay {
   bool mBreakAfter;     // [reset]
   uint8_t mOverflowX;           // [reset] see nsStyleConsts.h
   uint8_t mOverflowY;           // [reset] see nsStyleConsts.h
   uint8_t mOverflowClipBox;     // [reset] see nsStyleConsts.h
   uint8_t mResize;              // [reset] see nsStyleConsts.h
   uint8_t mClipFlags;           // [reset] see nsStyleConsts.h
   uint8_t mOrient;              // [reset] see nsStyleConsts.h
   uint8_t mMixBlendMode;        // [reset] see nsStyleConsts.h
+  uint8_t mIsolation;           // [reset] see nsStyleConsts.h
   uint8_t mWillChangeBitField;  // [reset] see nsStyleConsts.h. Stores a
                                 // bitfield representation of the properties
                                 // that are frequently queried. This should
                                 // match mWillChange. Also tracks if any of the
                                 // properties in the will-change list require
                                 // a stacking context.
   nsAutoTArray<nsString, 1> mWillChange;
 

--- a/layout/style/test/property_database.js
+++ b/layout/style/test/property_database.js
@@ -5509,16 +5509,27 @@ if (SpecialPowers.getBoolPref("layout.cs
     type: CSS_TYPE_LONGHAND,
     initial_values: [ "normal" ],
     other_values: ["multiply", "screen", "overlay", "darken", "lighten", "color-dodge", "color-burn",
         "hard-light", "soft-light", "difference", "exclusion", "hue", "saturation", "color", "luminosity"],
     invalid_values: []
   };
 }
 
+if (SpecialPowers.getBoolPref("layout.css.isolation.enabled")) {
+  gCSSProperties["isolation"] = {
+    domProp: "isolation",
+    inherited: false,
+    type: CSS_TYPE_LONGHAND,
+    initial_values: [ "auto" ],
+    other_values: ["isolated"],
+    invalid_values: []
+  };
+}
+
 if (SpecialPowers.getBoolPref("layout.css.background-blend-mode.enabled")) {
   gCSSProperties["background-blend-mode"] = {
     domProp: "backgroundBlendMode",
     inherited: false,
     type: CSS_TYPE_LONGHAND,
     initial_values: [ "normal" ],
     other_values: [ "multiply", "screen", "overlay", "darken", "lighten", "color-dodge", "color-burn",
       "hard-light", "soft-light", "difference", "exclusion", "hue", "saturation", "color", "luminosity" ],

--- a/layout/style/test/test_computed_style_prefs.html
+++ b/layout/style/test/test_computed_style_prefs.html
@@ -66,16 +66,17 @@ function step() {
 }
 
 // ----
 
 var gProps = {
   "layout.css.vertical-text.enabled": ["text-combine-upright", "text-orientation", "writing-mode"],
   "layout.css.image-orientation.enabled": ["image-orientation"],
   "layout.css.mix-blend-mode.enabled": ["mix-blend-mode"],
+  "layout.css.isolation.enabled": [ "isolation"],
   "layout.css.masking.enabled": ["mask-type"],
   "layout.css.touch_action.enabled": ["touch-action"]
 };
 
 var gCS = getComputedStyle(document.body, "");
 var gLengthWithAllPrefsDisabled;
 
 var gTestIndex = 0;

--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -2013,16 +2013,19 @@ pref("layout.css.dpi", -1);
 pref("layout.css.devPixelsPerPx", "-1.0");
 
 // Is support for CSS Masking features enabled?
 pref("layout.css.masking.enabled", true);
 
 // Is support for mix-blend-mode enabled?
 pref("layout.css.mix-blend-mode.enabled", true);
 
+// Is support for isolation enabled?
+pref("layout.css.isolation.enabled", false);
+
 // Is support for CSS Filters enabled?
 pref("layout.css.filters.enabled", true);
 
 // Is support for basic shapes in clip-path enabled?
 pref("layout.css.clip-path-shapes.enabled", false);
 
 // Is support for CSS sticky positioning enabled?
 pref("layout.css.sticky.enabled", true);