--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -141,16 +141,17 @@ using namespace mozilla::layout;
 using namespace mozilla::gfx;
 
 #define GRID_ENABLED_PREF_NAME "layout.css.grid.enabled"
 #define GRID_TEMPLATE_SUBGRID_ENABLED_PREF_NAME "layout.css.grid-template-subgrid-value.enabled"
 #define WEBKIT_PREFIXES_ENABLED_PREF_NAME "layout.css.prefixes.webkit"
 #define DISPLAY_CONTENTS_ENABLED_PREF_NAME "layout.css.display-contents.enabled"
 #define TEXT_ALIGN_UNSAFE_ENABLED_PREF_NAME "layout.css.text-align-unsafe-value.enabled"
 #define FLOAT_LOGICAL_VALUES_ENABLED_PREF_NAME "layout.css.float-logical-values.enabled"
+#define BG_CLIP_TEXT_ENABLED_PREF_NAME "layout.css.background-clip-text.enabled"
 
 #ifdef DEBUG
 // TODO: remove, see bug 598468.
 bool nsLayoutUtils::gPreventAssertInCompareTreePosition = false;
 #endif // DEBUG
 
 typedef FrameMetrics::ViewID ViewID;
 typedef nsStyleTransformMatrix::TransformReferenceBox TransformReferenceBox;
@@ -387,16 +388,45 @@ FloatLogicalValuesEnabledPrefChangeCallb
   MOZ_ASSERT(sIndexOfInlineStartInClearTable >= 0);
   nsCSSProps::kClearKTable[sIndexOfInlineStartInClearTable].mKeyword =
     isFloatLogicalValuesEnabled ? eCSSKeyword_inline_start : eCSSKeyword_UNKNOWN;
   MOZ_ASSERT(sIndexOfInlineEndInClearTable >= 0);
   nsCSSProps::kClearKTable[sIndexOfInlineEndInClearTable].mKeyword =
     isFloatLogicalValuesEnabled ? eCSSKeyword_inline_end : eCSSKeyword_UNKNOWN;
 }
 
+static void
+BackgroundClipTextEnabledPrefChangeCallback(const char* aPrefName,
+                                            void* aClosure)
+{
+  NS_ASSERTION(strcmp(aPrefName, BG_CLIP_TEXT_ENABLED_PREF_NAME) == 0,
+               "Did you misspell " BG_CLIP_TEXT_ENABLED_PREF_NAME " ?");
+
+  static bool sIsBGClipKeywordIndexInitialized;
+  static int32_t sIndexOfTextInBGClipTable;
+  bool isBGClipTextEnabled =
+    Preferences::GetBool(BG_CLIP_TEXT_ENABLED_PREF_NAME, false);
+
+  if (!sIsBGClipKeywordIndexInitialized) {
+    // First run: find the position of "text" in kBackgroundClipKTable.
+    sIndexOfTextInBGClipTable =
+      nsCSSProps::FindIndexOfKeyword(eCSSKeyword_text,
+                                     nsCSSProps::kBackgroundClipKTable);
+
+    sIsBGClipKeywordIndexInitialized = true;
+  }
+
+  // OK -- now, stomp on or restore the "text" entry in kBackgroundClipKTable,
+  // depending on whether the pref is enabled vs. disabled.
+  if (sIndexOfTextInBGClipTable >= 0) {
+    nsCSSProps::kBackgroundClipKTable[sIndexOfTextInBGClipTable].mKeyword =
+      isBGClipTextEnabled ? eCSSKeyword_text : eCSSKeyword_UNKNOWN;
+  }
+}
+
 template<typename TestType>
 static bool
 HasMatchingCurrentAnimations(const nsIFrame* aFrame, TestType&& aTest)
 {
   EffectSet* effects = EffectSet::GetEffectSet(aFrame);
   if (!effects) {
     return false;
   }
@@ -7638,16 +7668,20 @@ nsLayoutUtils::Initialize()
   DisplayContentsEnabledPrefChangeCallback(DISPLAY_CONTENTS_ENABLED_PREF_NAME,
                                            nullptr);
   TextAlignUnsafeEnabledPrefChangeCallback(TEXT_ALIGN_UNSAFE_ENABLED_PREF_NAME,
                                            nullptr);
   Preferences::RegisterCallback(FloatLogicalValuesEnabledPrefChangeCallback,
                                 FLOAT_LOGICAL_VALUES_ENABLED_PREF_NAME);
   FloatLogicalValuesEnabledPrefChangeCallback(FLOAT_LOGICAL_VALUES_ENABLED_PREF_NAME,
                                               nullptr);
+  Preferences::RegisterCallback(BackgroundClipTextEnabledPrefChangeCallback,
+                                BG_CLIP_TEXT_ENABLED_PREF_NAME);
+  BackgroundClipTextEnabledPrefChangeCallback(BG_CLIP_TEXT_ENABLED_PREF_NAME,
+                                              nullptr);
 
   nsComputedDOMStyle::RegisterPrefChangeCallbacks();
 }
 
 /* static */
 void
 nsLayoutUtils::Shutdown()
 {

--- a/layout/style/Declaration.cpp
+++ b/layout/style/Declaration.cpp
@@ -290,22 +290,26 @@ Declaration::GetImageLayerValue(
     }
 
     MOZ_ASSERT(clip->mValue.GetUnit() == eCSSUnit_Enumerated &&
                origin->mValue.GetUnit() == eCSSUnit_Enumerated,
                "should not have inherit/initial within list");
 
     if (clip->mValue.GetIntValue() != NS_STYLE_IMAGELAYER_CLIP_BORDER ||
         origin->mValue.GetIntValue() != NS_STYLE_IMAGELAYER_ORIGIN_PADDING) {
-      MOZ_ASSERT(nsCSSProps::kKeywordTableTable[
-                   aTable[nsStyleImageLayers::origin]] ==
-                 nsCSSProps::kImageLayerOriginKTable);
-      MOZ_ASSERT(nsCSSProps::kKeywordTableTable[
-                   aTable[nsStyleImageLayers::clip]] ==
-                 nsCSSProps::kImageLayerOriginKTable);
+#ifdef DEBUG
+      for (int i = 0; nsCSSProps::kImageLayerOriginKTable[i].mValue != -1 ; i++) {
+        // Ensure the keyword positions in origin and clip table are the same.
+        MOZ_ASSERT(nsCSSProps::kImageLayerOriginKTable[i].mKeyword ==
+                   nsCSSProps::kBackgroundClipKTable[i].mKeyword);
+        // Ensure the keyword values in origin and clip table are the same.
+        MOZ_ASSERT(nsCSSProps::kImageLayerOriginKTable[i].mValue ==
+                   nsCSSProps::kBackgroundClipKTable[i].mValue);
+      }
+#endif
       static_assert(NS_STYLE_IMAGELAYER_CLIP_BORDER ==
                     NS_STYLE_IMAGELAYER_ORIGIN_BORDER &&
                     NS_STYLE_IMAGELAYER_CLIP_PADDING ==
                     NS_STYLE_IMAGELAYER_ORIGIN_PADDING &&
                     NS_STYLE_IMAGELAYER_CLIP_CONTENT ==
                     NS_STYLE_IMAGELAYER_ORIGIN_CONTENT,
                     "mask-clip and mask-origin style constants must agree");
       aValue.Append(char16_t(' '));

--- a/layout/style/nsCSSParser.cpp
+++ b/layout/style/nsCSSParser.cpp
@@ -12055,23 +12055,26 @@ CSSParserImpl::ParseImageLayersItem(
             CSSParseResult::Ok) {
           NS_NOTREACHED("should be able to parse");
           return false;
         }
 
         // The spec allows a second box value (for background-clip),
         // immediately following the first one (for background-origin).
 
-        // 'background-clip' and 'background-origin' use the same keyword table
-        MOZ_ASSERT(nsCSSProps::kKeywordTableTable[
-                     aTable[nsStyleImageLayers::origin]] ==
-                   nsCSSProps::kImageLayerOriginKTable);
-        MOZ_ASSERT(nsCSSProps::kKeywordTableTable[
-                     aTable[nsStyleImageLayers::clip]] ==
-                   nsCSSProps::kImageLayerOriginKTable);
+#ifdef DEBUG
+        for (int i = 0; nsCSSProps::kImageLayerOriginKTable[i].mValue != -1 ; i++) {
+          // Ensure the keyword positions in origin and clip table are the same.
+          MOZ_ASSERT(nsCSSProps::kImageLayerOriginKTable[i].mKeyword ==
+                     nsCSSProps::kBackgroundClipKTable[i].mKeyword);
+          // Ensure the keyword values in origin and clip table are the same.
+          MOZ_ASSERT(nsCSSProps::kImageLayerOriginKTable[i].mValue ==
+                     nsCSSProps::kBackgroundClipKTable[i].mValue);
+        }
+#endif
         static_assert(NS_STYLE_IMAGELAYER_CLIP_BORDER ==
                       NS_STYLE_IMAGELAYER_ORIGIN_BORDER &&
                       NS_STYLE_IMAGELAYER_CLIP_PADDING ==
                       NS_STYLE_IMAGELAYER_ORIGIN_PADDING &&
                       NS_STYLE_IMAGELAYER_CLIP_CONTENT ==
                       NS_STYLE_IMAGELAYER_ORIGIN_CONTENT,
                       "bg-clip and bg-origin style constants must agree");
 

--- a/layout/style/nsCSSPropList.h
+++ b/layout/style/nsCSSPropList.h
@@ -545,17 +545,17 @@ CSS_PROP_BACKGROUND(
     background_clip,
     BackgroundClip,
     CSS_PROPERTY_PARSE_VALUE_LIST |
         CSS_PROPERTY_APPLIES_TO_FIRST_LETTER_AND_FIRST_LINE |
         CSS_PROPERTY_APPLIES_TO_PLACEHOLDER |
         CSS_PROPERTY_VALUE_LIST_USES_COMMAS,
     "",
     VARIANT_KEYWORD, // used by list parsing
-    kImageLayerOriginKTable,
+    kBackgroundClipKTable,
     CSS_PROP_NO_OFFSET,
     eStyleAnimType_None)
 CSS_PROP_BACKGROUND(
     background-color,
     background_color,
     BackgroundColor,
     CSS_PROPERTY_PARSE_VALUE |
         CSS_PROPERTY_APPLIES_TO_FIRST_LETTER_AND_FIRST_LINE |

--- a/layout/style/nsCSSProps.cpp
+++ b/layout/style/nsCSSProps.cpp
@@ -885,24 +885,41 @@ const KTableEntry nsCSSProps::kImageLaye
   { eCSSKeyword_scroll, NS_STYLE_IMAGELAYER_ATTACHMENT_SCROLL },
   { eCSSKeyword_local, NS_STYLE_IMAGELAYER_ATTACHMENT_LOCAL },
   { eCSSKeyword_UNKNOWN, -1 }
 };
 
 static_assert(NS_STYLE_IMAGELAYER_CLIP_BORDER == NS_STYLE_IMAGELAYER_ORIGIN_BORDER &&
               NS_STYLE_IMAGELAYER_CLIP_PADDING == NS_STYLE_IMAGELAYER_ORIGIN_PADDING &&
               NS_STYLE_IMAGELAYER_CLIP_CONTENT == NS_STYLE_IMAGELAYER_ORIGIN_CONTENT,
-              "bg-clip and bg-origin style constants must agree");
+              "Except background-clip:text, all the other background-clip and "
+              "background-origin style constants must agree");
+
 const KTableEntry nsCSSProps::kImageLayerOriginKTable[] = {
   { eCSSKeyword_border_box, NS_STYLE_IMAGELAYER_ORIGIN_BORDER },
   { eCSSKeyword_padding_box, NS_STYLE_IMAGELAYER_ORIGIN_PADDING },
   { eCSSKeyword_content_box, NS_STYLE_IMAGELAYER_ORIGIN_CONTENT },
   { eCSSKeyword_UNKNOWN, -1 }
 };
 
+KTableEntry nsCSSProps::kBackgroundClipKTable[] = {
+  { eCSSKeyword_border_box, NS_STYLE_IMAGELAYER_CLIP_BORDER },
+  { eCSSKeyword_padding_box, NS_STYLE_IMAGELAYER_CLIP_PADDING },
+  { eCSSKeyword_content_box, NS_STYLE_IMAGELAYER_CLIP_CONTENT },
+  // The next entry is controlled by the layout.css.background-clip-text.enabled
+  // pref.
+  { eCSSKeyword_text, NS_STYLE_IMAGELAYER_CLIP_TEXT },
+  { eCSSKeyword_UNKNOWN, -1 }
+};
+
+static_assert(ArrayLength(nsCSSProps::kImageLayerOriginKTable) ==
+              ArrayLength(nsCSSProps::kBackgroundClipKTable) - 1,
+              "background-clip has one more extra value, which is text, compare"
+              "to background-origin");
+
 // Note: Don't change this table unless you update
 // ParseImageLayerPosition!
 
 const KTableEntry nsCSSProps::kImageLayerPositionKTable[] = {
   { eCSSKeyword_center, NS_STYLE_IMAGELAYER_POSITION_CENTER },
   { eCSSKeyword_top, NS_STYLE_IMAGELAYER_POSITION_TOP },
   { eCSSKeyword_bottom, NS_STYLE_IMAGELAYER_POSITION_BOTTOM },
   { eCSSKeyword_left, NS_STYLE_IMAGELAYER_POSITION_LEFT },

--- a/layout/style/nsCSSProps.h
+++ b/layout/style/nsCSSProps.h
@@ -673,16 +673,19 @@ public:
   static const KTableEntry kImageLayerAttachmentKTable[];
   static const KTableEntry kImageLayerOriginKTable[];
   static const KTableEntry kImageLayerPositionKTable[];
   static const KTableEntry kImageLayerRepeatKTable[];
   static const KTableEntry kImageLayerRepeatPartKTable[];
   static const KTableEntry kImageLayerSizeKTable[];
   static const KTableEntry kImageLayerCompositeKTable[];
   static const KTableEntry kImageLayerModeKTable[];
+  // Not const because we modify its entries when the pref
+  // "layout.css.background-clip.text" changes:
+  static KTableEntry kBackgroundClipKTable[];
   static const KTableEntry kBlendModeKTable[];
   static const KTableEntry kBorderCollapseKTable[];
   static const KTableEntry kBorderColorKTable[];
   static const KTableEntry kBorderImageRepeatKTable[];
   static const KTableEntry kBorderImageSliceKTable[];
   static const KTableEntry kBorderStyleKTable[];
   static const KTableEntry kBorderWidthKTable[];
   static const KTableEntry kBoxAlignKTable[];

--- a/layout/style/nsComputedDOMStyle.cpp
+++ b/layout/style/nsComputedDOMStyle.cpp
@@ -1840,17 +1840,17 @@ nsComputedDOMStyle::DoGetBackgroundAttac
 }
 
 already_AddRefed<CSSValue>
 nsComputedDOMStyle::DoGetBackgroundClip()
 {
   return GetBackgroundList(&nsStyleImageLayers::Layer::mClip,
                            &nsStyleImageLayers::mClipCount,
                            StyleBackground()->mImage,
-                           nsCSSProps::kImageLayerOriginKTable);
+                           nsCSSProps::kBackgroundClipKTable);
 }
 
 already_AddRefed<CSSValue>
 nsComputedDOMStyle::DoGetBackgroundColor()
 {
   RefPtr<nsROCSSPrimitiveValue> val = new nsROCSSPrimitiveValue;
   SetToRGBAColor(val, StyleBackground()->mBackgroundColor);
   return val.forget();

--- a/layout/style/nsStyleConsts.h
+++ b/layout/style/nsStyleConsts.h
@@ -262,20 +262,22 @@ enum class FillMode : uint32_t;
 #define NS_STYLE_ANIMATION_PLAY_STATE_PAUSED      1
 
 // See nsStyleImageLayers
 #define NS_STYLE_IMAGELAYER_ATTACHMENT_SCROLL        0
 #define NS_STYLE_IMAGELAYER_ATTACHMENT_FIXED         1
 #define NS_STYLE_IMAGELAYER_ATTACHMENT_LOCAL         2
 
 // See nsStyleImageLayers
-// Code depends on these constants having the same values as BG_ORIGIN_*
+// Code depends on these constants having the same values as IMAGELAYER_ORIGIN_*
 #define NS_STYLE_IMAGELAYER_CLIP_BORDER              0
 #define NS_STYLE_IMAGELAYER_CLIP_PADDING             1
 #define NS_STYLE_IMAGELAYER_CLIP_CONTENT             2
+// One extra constant which does not exist in IMAGELAYER_ORIGIN_*
+#define NS_STYLE_IMAGELAYER_CLIP_TEXT                3
 
 // A magic value that we use for our "pretend that background-clip is
 // 'padding' when we have a solid border" optimization.  This isn't
 // actually equal to NS_STYLE_IMAGELAYER_CLIP_PADDING because using that
 // causes antialiasing seams between the background and border.  This
 // is a backend-only value.
 #define NS_STYLE_IMAGELAYER_CLIP_MOZ_ALMOST_PADDING  127
 

--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -2417,16 +2417,20 @@ pref("layout.css.unprefixing-service.glo
 #endif
 
 // Is support for the :scope selector enabled?
 pref("layout.css.scope-pseudo.enabled", true);
 
 // Is support for background-blend-mode enabled?
 pref("layout.css.background-blend-mode.enabled", true);
 
+// Keep this disabled on for now. See bug 1263516.
+// Is support for background-clip:text enabled?
+pref("layout.css.background-clip-text.enabled", false);
+
 // Is support for CSS vertical text enabled?
 pref("layout.css.vertical-text.enabled", true);
 
 // Is support for CSS text-combine-upright (tate-chu-yoko) enabled?
 pref("layout.css.text-combine-upright.enabled", false);
 
 // Is support for object-fit and object-position enabled?
 pref("layout.css.object-fit-and-position.enabled", true);