--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -142,17 +142,16 @@ using namespace mozilla::dom;
 using namespace mozilla::image;
 using namespace mozilla::layers;
 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"
 
 // The time in number of frames that we estimate for a refresh driver
 // to be quiescent
 #define DEFAULT_QUIESCENT_FRAMES 2
 // The time (milliseconds) we estimate is needed between the end of an
@@ -307,46 +306,16 @@ WebkitPrefixEnabledPrefChangeCallback(co
   }
   if (sIndexOfWebkitInlineFlexInDisplayTable >= 0) {
     nsCSSProps::kDisplayKTable[sIndexOfWebkitInlineFlexInDisplayTable].mKeyword =
       isWebkitPrefixSupportEnabled ?
       eCSSKeyword__webkit_inline_flex : eCSSKeyword_UNKNOWN;
   }
 }
 
-// When the pref "layout.css.display-contents.enabled" changes, this function is
-// invoked to let us update kDisplayKTable, to selectively disable or restore
-// the entries for "contents" in that table.
-static void
-DisplayContentsEnabledPrefChangeCallback(const char* aPrefName, void* aClosure)
-{
-  NS_ASSERTION(strcmp(aPrefName, DISPLAY_CONTENTS_ENABLED_PREF_NAME) == 0,
-               "Did you misspell " DISPLAY_CONTENTS_ENABLED_PREF_NAME " ?");
-
-  static bool sIsDisplayContentsKeywordIndexInitialized;
-  static int32_t sIndexOfContentsInDisplayTable;
-  bool isDisplayContentsEnabled =
-    Preferences::GetBool(DISPLAY_CONTENTS_ENABLED_PREF_NAME, false);
-
-  if (!sIsDisplayContentsKeywordIndexInitialized) {
-    // First run: find the position of "contents" in kDisplayKTable.
-    sIndexOfContentsInDisplayTable =
-      nsCSSProps::FindIndexOfKeyword(eCSSKeyword_contents,
-                                     nsCSSProps::kDisplayKTable);
-    sIsDisplayContentsKeywordIndexInitialized = true;
-  }
-
-  // OK -- now, stomp on or restore the "contents" entry in kDisplayKTable,
-  // depending on whether the pref is enabled vs. disabled.
-  if (sIndexOfContentsInDisplayTable >= 0) {
-    nsCSSProps::kDisplayKTable[sIndexOfContentsInDisplayTable].mKeyword =
-      isDisplayContentsEnabled ? eCSSKeyword_contents : eCSSKeyword_UNKNOWN;
-  }
-}
-
 // When the pref "layout.css.text-align-unsafe-value.enabled" changes, this
 // function is called to let us update kTextAlignKTable & kTextAlignLastKTable,
 // to selectively disable or restore the entries for "unsafe" in those tables.
 static void
 TextAlignUnsafeEnabledPrefChangeCallback(const char* aPrefName, void* aClosure)
 {
   NS_ASSERTION(strcmp(aPrefName, TEXT_ALIGN_UNSAFE_ENABLED_PREF_NAME) == 0,
                "Did you misspell " TEXT_ALIGN_UNSAFE_ENABLED_PREF_NAME " ?");
@@ -7529,18 +7498,16 @@ struct PrefCallbacks
 };
 static const PrefCallbacks kPrefCallbacks[] = {
   { GRID_ENABLED_PREF_NAME,
     GridEnabledPrefChangeCallback },
   { WEBKIT_PREFIXES_ENABLED_PREF_NAME,
     WebkitPrefixEnabledPrefChangeCallback },
   { TEXT_ALIGN_UNSAFE_ENABLED_PREF_NAME,
     TextAlignUnsafeEnabledPrefChangeCallback },
-  { DISPLAY_CONTENTS_ENABLED_PREF_NAME,
-    DisplayContentsEnabledPrefChangeCallback },
   { FLOAT_LOGICAL_VALUES_ENABLED_PREF_NAME,
     FloatLogicalValuesEnabledPrefChangeCallback },
   { BG_CLIP_TEXT_ENABLED_PREF_NAME,
     BackgroundClipTextEnabledPrefChangeCallback },
 };
 
 /* static */
 void

--- a/layout/reftests/css-display/reftest-stylo.list
+++ b/layout/reftests/css-display/reftest-stylo.list
@@ -1,37 +1,37 @@
 # DO NOT EDIT! This is a auto-generated temporary list for Stylo testing
 # Tests for CSS Display spec features.
 # http://dev.w3.org/csswg/css-display
 
-fuzzy-if(Android,8,604) pref(layout.css.display-contents.enabled,true) == display-contents-acid.html display-contents-acid.html
-random pref(layout.css.display-contents.enabled,true) == display-contents-acid-dyn-1.html display-contents-acid-dyn-1.html
-random pref(layout.css.display-contents.enabled,true) == display-contents-acid-dyn-2.html display-contents-acid-dyn-2.html
-random pref(layout.css.display-contents.enabled,true) == display-contents-acid-dyn-3.html display-contents-acid-dyn-3.html
-pref(layout.css.display-contents.enabled,true) == display-contents-generated-content.html display-contents-generated-content.html
-pref(layout.css.display-contents.enabled,true) == display-contents-generated-content-2.html display-contents-generated-content-2.html
-pref(layout.css.display-contents.enabled,true) == display-contents-style-inheritance-1.html display-contents-style-inheritance-1.html
-skip pref(layout.css.display-contents.enabled,true) == display-contents-style-inheritance-1-stylechange.html display-contents-style-inheritance-1-stylechange.html
-skip pref(layout.css.display-contents.enabled,true) fuzzy-if(winWidget,12,100) == display-contents-style-inheritance-1-dom-mutations.html display-contents-style-inheritance-1-dom-mutations.html
-pref(layout.css.display-contents.enabled,true) == display-contents-tables.xhtml display-contents-tables.xhtml
-pref(layout.css.display-contents.enabled,true) == display-contents-tables-2.xhtml display-contents-tables-2.xhtml
-pref(layout.css.display-contents.enabled,true) == display-contents-tables-3.xhtml display-contents-tables-3.xhtml
-pref(layout.css.display-contents.enabled,true) == display-contents-visibility-hidden.html display-contents-visibility-hidden.html
-pref(layout.css.display-contents.enabled,true) == display-contents-visibility-hidden-2.html display-contents-visibility-hidden-2.html
-random pref(layout.css.display-contents.enabled,true) == display-contents-495385-2d.html display-contents-495385-2d.html
-skip-if(B2G||Mulet) fuzzy-if(Android,7,3935) pref(layout.css.display-contents.enabled,true) == display-contents-xbl.xhtml display-contents-xbl.xhtml
+fuzzy-if(Android,8,604) == display-contents-acid.html display-contents-acid.html
+random == display-contents-acid-dyn-1.html display-contents-acid-dyn-1.html
+random == display-contents-acid-dyn-2.html display-contents-acid-dyn-2.html
+random == display-contents-acid-dyn-3.html display-contents-acid-dyn-3.html
+== display-contents-generated-content.html display-contents-generated-content.html
+== display-contents-generated-content-2.html display-contents-generated-content-2.html
+== display-contents-style-inheritance-1.html display-contents-style-inheritance-1.html
+skip == display-contents-style-inheritance-1-stylechange.html display-contents-style-inheritance-1-stylechange.html
+skip fuzzy-if(winWidget,12,100) == display-contents-style-inheritance-1-dom-mutations.html display-contents-style-inheritance-1-dom-mutations.html
+== display-contents-tables.xhtml display-contents-tables.xhtml
+== display-contents-tables-2.xhtml display-contents-tables-2.xhtml
+== display-contents-tables-3.xhtml display-contents-tables-3.xhtml
+== display-contents-visibility-hidden.html display-contents-visibility-hidden.html
+== display-contents-visibility-hidden-2.html display-contents-visibility-hidden-2.html
+random == display-contents-495385-2d.html display-contents-495385-2d.html
+skip-if(B2G||Mulet) fuzzy-if(Android,7,3935) == display-contents-xbl.xhtml display-contents-xbl.xhtml
 # Initial mulet triage: parity with B2G/B2G Desktop
-# fuzzy-if(Android,7,1186) pref(layout.css.display-contents.enabled,true) pref(dom.webcomponents.enabled,true) == display-contents-shadow-dom-1.html display-contents-shadow-dom-1.html
-skip-if(B2G||Mulet) pref(layout.css.display-contents.enabled,true) == display-contents-xbl-2.xul display-contents-xbl-2.xul
+# fuzzy-if(Android,7,1186) pref(dom.webcomponents.enabled,true) == display-contents-shadow-dom-1.html display-contents-shadow-dom-1.html
+skip-if(B2G||Mulet) == display-contents-xbl-2.xul display-contents-xbl-2.xul
 # Initial mulet triage: parity with B2G/B2G Desktop
-skip-if(B2G||Mulet) asserts(1) pref(layout.css.display-contents.enabled,true) == display-contents-xbl-3.xul display-contents-xbl-3.xul
+skip-if(B2G||Mulet) asserts(1) == display-contents-xbl-3.xul display-contents-xbl-3.xul
 # bug 1089223
 # Initial mulet triage: parity with B2G/B2G Desktop
-skip pref(layout.css.display-contents.enabled,true) == display-contents-xbl-4.xul display-contents-xbl-4.xul
+skip == display-contents-xbl-4.xul display-contents-xbl-4.xul
 # fails (not just asserts) due to bug 1089223
-asserts(0-1) fuzzy-if(Android,8,3216) pref(layout.css.display-contents.enabled,true) == display-contents-fieldset.html display-contents-fieldset.html
+asserts(0-1) fuzzy-if(Android,8,3216) == display-contents-fieldset.html display-contents-fieldset.html
 # bug 1089223
-skip-if(B2G||Mulet) asserts(1) pref(layout.css.display-contents.enabled,true) == display-contents-xbl-5.xul display-contents-xbl-5.xul
+skip-if(B2G||Mulet) asserts(1) == display-contents-xbl-5.xul display-contents-xbl-5.xul
 # bug 1089223
 # Initial mulet triage: parity with B2G/B2G Desktop
-pref(layout.css.display-contents.enabled,true) == display-contents-list-item-child.html display-contents-list-item-child.html
-pref(layout.css.display-contents.enabled,true) == display-contents-writing-mode-1.html display-contents-writing-mode-1.html
-pref(layout.css.display-contents.enabled,true) == display-contents-writing-mode-2.html display-contents-writing-mode-2.html
+== display-contents-list-item-child.html display-contents-list-item-child.html
+== display-contents-writing-mode-1.html display-contents-writing-mode-1.html
+== display-contents-writing-mode-2.html display-contents-writing-mode-2.html

--- a/layout/reftests/css-display/reftest.list
+++ b/layout/reftests/css-display/reftest.list
@@ -1,28 +1,28 @@
 # Tests for CSS Display spec features.
 # http://dev.w3.org/csswg/css-display
 
-fuzzy-if(Android,8,604) pref(layout.css.display-contents.enabled,true) == display-contents-acid.html display-contents-acid-ref.html
-fuzzy-if(Android,8,604) pref(layout.css.display-contents.enabled,true) == display-contents-acid-dyn-1.html display-contents-acid-ref.html
-fuzzy-if(Android,8,604) pref(layout.css.display-contents.enabled,true) == display-contents-acid-dyn-2.html display-contents-acid-ref.html
-fuzzy-if(Android,8,604) pref(layout.css.display-contents.enabled,true) == display-contents-acid-dyn-3.html display-contents-acid-ref.html
-pref(layout.css.display-contents.enabled,true) == display-contents-generated-content.html display-contents-generated-content-ref.html
-pref(layout.css.display-contents.enabled,true) == display-contents-generated-content-2.html display-contents-generated-content-ref.html
-pref(layout.css.display-contents.enabled,true) == display-contents-style-inheritance-1.html display-contents-style-inheritance-1-ref.html
-pref(layout.css.display-contents.enabled,true) == display-contents-style-inheritance-1-stylechange.html display-contents-style-inheritance-1-ref.html
-pref(layout.css.display-contents.enabled,true) fuzzy-if(winWidget,12,100) == display-contents-style-inheritance-1-dom-mutations.html display-contents-style-inheritance-1-ref.html
-pref(layout.css.display-contents.enabled,true) == display-contents-tables.xhtml display-contents-tables-ref.xhtml
-pref(layout.css.display-contents.enabled,true) == display-contents-tables-2.xhtml display-contents-tables-ref.xhtml
-pref(layout.css.display-contents.enabled,true) == display-contents-tables-3.xhtml display-contents-tables-3-ref.xhtml
-pref(layout.css.display-contents.enabled,true) == display-contents-visibility-hidden.html display-contents-visibility-hidden-ref.html
-pref(layout.css.display-contents.enabled,true) == display-contents-visibility-hidden-2.html display-contents-visibility-hidden-ref.html
-pref(layout.css.display-contents.enabled,true) == display-contents-495385-2d.html display-contents-495385-2d-ref.html
-fuzzy-if(Android,7,3935) pref(layout.css.display-contents.enabled,true) == display-contents-xbl.xhtml display-contents-xbl-ref.html
-fuzzy-if(Android,7,1186) pref(layout.css.display-contents.enabled,true) pref(dom.webcomponents.enabled,true) == display-contents-shadow-dom-1.html display-contents-shadow-dom-1-ref.html
-pref(layout.css.display-contents.enabled,true) == display-contents-xbl-2.xul display-contents-xbl-2-ref.xul
-asserts(1) pref(layout.css.display-contents.enabled,true) == display-contents-xbl-3.xul display-contents-xbl-3-ref.xul # bug 1089223
-skip pref(layout.css.display-contents.enabled,true) == display-contents-xbl-4.xul display-contents-xbl-4-ref.xul # fails (not just asserts) due to bug 1089223
-asserts(0-1) fuzzy-if(Android,8,3216) pref(layout.css.display-contents.enabled,true) == display-contents-fieldset.html display-contents-fieldset-ref.html # bug 1089223
-asserts(1) pref(layout.css.display-contents.enabled,true) == display-contents-xbl-5.xul display-contents-xbl-3-ref.xul # bug 1089223
-pref(layout.css.display-contents.enabled,true) == display-contents-list-item-child.html display-contents-list-item-child-ref.html
-pref(layout.css.display-contents.enabled,true) == display-contents-writing-mode-1.html display-contents-writing-mode-1-ref.html
-pref(layout.css.display-contents.enabled,true) == display-contents-writing-mode-2.html display-contents-writing-mode-2-ref.html
+fuzzy-if(Android,8,604) == display-contents-acid.html display-contents-acid-ref.html
+fuzzy-if(Android,8,604) == display-contents-acid-dyn-1.html display-contents-acid-ref.html
+fuzzy-if(Android,8,604) == display-contents-acid-dyn-2.html display-contents-acid-ref.html
+fuzzy-if(Android,8,604) == display-contents-acid-dyn-3.html display-contents-acid-ref.html
+== display-contents-generated-content.html display-contents-generated-content-ref.html
+== display-contents-generated-content-2.html display-contents-generated-content-ref.html
+== display-contents-style-inheritance-1.html display-contents-style-inheritance-1-ref.html
+== display-contents-style-inheritance-1-stylechange.html display-contents-style-inheritance-1-ref.html
+fuzzy-if(winWidget,12,100) == display-contents-style-inheritance-1-dom-mutations.html display-contents-style-inheritance-1-ref.html
+== display-contents-tables.xhtml display-contents-tables-ref.xhtml
+== display-contents-tables-2.xhtml display-contents-tables-ref.xhtml
+== display-contents-tables-3.xhtml display-contents-tables-3-ref.xhtml
+== display-contents-visibility-hidden.html display-contents-visibility-hidden-ref.html
+== display-contents-visibility-hidden-2.html display-contents-visibility-hidden-ref.html
+== display-contents-495385-2d.html display-contents-495385-2d-ref.html
+fuzzy-if(Android,7,3935) == display-contents-xbl.xhtml display-contents-xbl-ref.html
+fuzzy-if(Android,7,1186) pref(dom.webcomponents.enabled,true) == display-contents-shadow-dom-1.html display-contents-shadow-dom-1-ref.html
+== display-contents-xbl-2.xul display-contents-xbl-2-ref.xul
+asserts(1) == display-contents-xbl-3.xul display-contents-xbl-3-ref.xul # bug 1089223
+skip == display-contents-xbl-4.xul display-contents-xbl-4-ref.xul # fails (not just asserts) due to bug 1089223
+asserts(0-1) fuzzy-if(Android,8,3216) == display-contents-fieldset.html display-contents-fieldset-ref.html # bug 1089223
+asserts(1) == display-contents-xbl-5.xul display-contents-xbl-3-ref.xul # bug 1089223
+== display-contents-list-item-child.html display-contents-list-item-child-ref.html
+== display-contents-writing-mode-1.html display-contents-writing-mode-1-ref.html
+== display-contents-writing-mode-2.html display-contents-writing-mode-2-ref.html

--- a/layout/style/nsCSSProps.cpp
+++ b/layout/style/nsCSSProps.cpp
@@ -1325,18 +1325,16 @@ KTableEntry nsCSSProps::kDisplayKTable[]
   // The next two entries are controlled by the layout.css.grid.enabled pref.
   { eCSSKeyword_grid,                StyleDisplay::Grid },
   { eCSSKeyword_inline_grid,         StyleDisplay::InlineGrid },
   // The next 4 entries are controlled by the layout.css.prefixes.webkit pref.
   { eCSSKeyword__webkit_box,         StyleDisplay::WebkitBox },
   { eCSSKeyword__webkit_inline_box,  StyleDisplay::WebkitInlineBox },
   { eCSSKeyword__webkit_flex,        StyleDisplay::Flex },
   { eCSSKeyword__webkit_inline_flex, StyleDisplay::InlineFlex },
-  // The next entry is controlled by the layout.css.display-contents.enabled
-  // pref.
   { eCSSKeyword_contents,            StyleDisplay::Contents },
   { eCSSKeyword_UNKNOWN,             -1 }
 };
 
 const KTableEntry nsCSSProps::kEmptyCellsKTable[] = {
   { eCSSKeyword_show,                 NS_STYLE_TABLE_EMPTY_CELLS_SHOW },
   { eCSSKeyword_hide,                 NS_STYLE_TABLE_EMPTY_CELLS_HIDE },
   { eCSSKeyword_UNKNOWN,              -1 }

--- a/layout/style/test/property_database.js
+++ b/layout/style/test/property_database.js
@@ -6666,19 +6666,17 @@ if (IsCSSPropertyPrefEnabled("layout.css
     subproperties: [ "grid-column-gap", "grid-row-gap" ],
     initial_values: [ "0", "0 0" ],
     other_values: [ "1ch 0", "1px 1%", "1em 1px", "calc(1px) calc(1%)" ],
     invalid_values: [ "-1px", "1px -1px", "1px 1px 1px", "inherit 1px",
                       "1px auto" ]
   };
 }
 
-if (IsCSSPropertyPrefEnabled("layout.css.display-contents.enabled")) {
-  gCSSProperties["display"].other_values.push("contents");
-}
+gCSSProperties["display"].other_values.push("contents");
 
 if (IsCSSPropertyPrefEnabled("layout.css.contain.enabled")) {
   gCSSProperties["contain"] = {
     domProp: "contain",
     inherited: false,
     type: CSS_TYPE_LONGHAND,
     initial_values: [ "none" ],
     other_values: [

--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -2612,19 +2612,16 @@ pref("layout.css.grid.enabled", true);
 #endif
 
 // Is support for CSS "grid-template-{columns,rows}: subgrid X" enabled?
 pref("layout.css.grid-template-subgrid-value.enabled", false);
 
 // Is support for CSS contain enabled?
 pref("layout.css.contain.enabled", false);
 
-// Is support for CSS display:contents enabled?
-pref("layout.css.display-contents.enabled", true);
-
 // Is support for CSS box-decoration-break enabled?
 pref("layout.css.box-decoration-break.enabled", true);
 
 // Is layout of CSS outline-style:auto enabled?
 pref("layout.css.outline-style-auto.enabled", false);
 
 // Is CSSOM-View scroll-behavior and its MSD smooth scrolling enabled?
 pref("layout.css.scroll-behavior.enabled", true);