diff --git a/layout/style/Declaration.cpp b/layout/style/Declaration.cpp
index 42131474b9f..be5cf21bce7 100644
--- a/layout/style/Declaration.cpp
+++ b/layout/style/Declaration.cpp
@@ -13,6 +13,7 @@
 
 #include "mozilla/css/Declaration.h"
 #include "nsPrintfCString.h"
+#include "mozilla/Preferences.h"
 
 namespace mozilla {
 namespace css {
@@ -178,6 +179,9 @@ Declaration::GetValue(nsCSSProperty aProperty, nsAString& aValue) const
       // The system-font subproperty and the *-source properties don't count.
       continue;
     }
+    if (!nsCSSProps::IsEnabled(*p)) {
+      continue;
+    }
     ++totalCount;
     const nsCSSValue *val = mData->ValueFor(*p);
     NS_ABORT_IF_FALSE(!val || !mImportantData || !mImportantData->ValueFor(*p),
@@ -564,6 +568,9 @@ Declaration::GetValue(nsCSSProperty aProperty, nsAString& aValue) const
       const nsCSSValue &fontVariantPosition =
         *data->ValueFor(eCSSProperty_font_variant_position);
 
+      bool fontFeaturesEnabled =
+        mozilla::Preferences::GetBool("layout.css.font-features.enabled");
+
       if (systemFont &&
           systemFont->GetUnit() != eCSSUnit_None &&
           systemFont->GetUnit() != eCSSUnit_Null) {
@@ -577,39 +584,38 @@ Declaration::GetValue(nsCSSProperty aProperty, nsAString& aValue) const
             sizeAdjust.GetUnit() != eCSSUnit_System_Font ||
             featureSettings.GetUnit() != eCSSUnit_System_Font ||
             languageOverride.GetUnit() != eCSSUnit_System_Font ||
-            fontKerning.GetUnit() != eCSSUnit_System_Font ||
-            fontSynthesis.GetUnit() != eCSSUnit_System_Font ||
-            fontVariantAlternates.GetUnit() != eCSSUnit_System_Font ||
-            fontVariantCaps.GetUnit() != eCSSUnit_System_Font ||
-            fontVariantEastAsian.GetUnit() != eCSSUnit_System_Font ||
-            fontVariantLigatures.GetUnit() != eCSSUnit_System_Font ||
-            fontVariantNumeric.GetUnit() != eCSSUnit_System_Font ||
-            fontVariantPosition.GetUnit() != eCSSUnit_System_Font) {
+            (fontFeaturesEnabled &&
+             (fontKerning.GetUnit() != eCSSUnit_System_Font ||
+              fontSynthesis.GetUnit() != eCSSUnit_System_Font ||
+              fontVariantAlternates.GetUnit() != eCSSUnit_System_Font ||
+              fontVariantCaps.GetUnit() != eCSSUnit_System_Font ||
+              fontVariantEastAsian.GetUnit() != eCSSUnit_System_Font ||
+              fontVariantLigatures.GetUnit() != eCSSUnit_System_Font ||
+              fontVariantNumeric.GetUnit() != eCSSUnit_System_Font ||
+              fontVariantPosition.GetUnit() != eCSSUnit_System_Font))) {
           // This can't be represented as a shorthand.
           return;
         }
         systemFont->AppendToString(eCSSProperty__x_system_font, aValue);
       } else {
-        // The font-stretch, font-size-adjust,
-        // -moz-font-feature-settings, -moz-font-language-override
-        // along with kerning, synthesis and other font-variant
-        // subproperties are reset by this shorthand property to their
-        // initial values, but can't be represented in its syntax.
+        // properties reset by this shorthand property to their
+        // initial values but not represented in its syntax
         if (stretch.GetUnit() != eCSSUnit_Enumerated ||
             stretch.GetIntValue() != NS_STYLE_FONT_STRETCH_NORMAL ||
             sizeAdjust.GetUnit() != eCSSUnit_None ||
             featureSettings.GetUnit() != eCSSUnit_Normal ||
             languageOverride.GetUnit() != eCSSUnit_Normal ||
-            fontKerning.GetIntValue() != NS_FONT_KERNING_AUTO ||
-            fontSynthesis.GetUnit() != eCSSUnit_Enumerated ||
-            fontSynthesis.GetIntValue() !=
-              (NS_FONT_SYNTHESIS_WEIGHT | NS_FONT_SYNTHESIS_STYLE) ||
-            fontVariantAlternates.GetUnit() != eCSSUnit_Normal ||
-            fontVariantCaps.GetUnit() != eCSSUnit_Normal ||
-            fontVariantEastAsian.GetUnit() != eCSSUnit_Normal ||
-            fontVariantLigatures.GetUnit() != eCSSUnit_Normal ||
-            fontVariantNumeric.GetUnit() != eCSSUnit_Normal ||
-            fontVariantPosition.GetUnit() != eCSSUnit_Normal) {
+            (fontFeaturesEnabled &&
+             (fontKerning.GetIntValue() != NS_FONT_KERNING_AUTO ||
+              fontSynthesis.GetUnit() != eCSSUnit_Enumerated ||
+              fontSynthesis.GetIntValue() !=
+                (NS_FONT_SYNTHESIS_WEIGHT | NS_FONT_SYNTHESIS_STYLE) ||
+              fontVariantAlternates.GetUnit() != eCSSUnit_Normal ||
+              fontVariantCaps.GetUnit() != eCSSUnit_Normal ||
+              fontVariantEastAsian.GetUnit() != eCSSUnit_Normal ||
+              fontVariantLigatures.GetUnit() != eCSSUnit_Normal ||
+              fontVariantNumeric.GetUnit() != eCSSUnit_Normal ||
+              fontVariantPosition.GetUnit() != eCSSUnit_Normal))) {
           return;
         }
 
@@ -956,6 +962,9 @@ Declaration::ToString(nsAString& aString) const
   nsAutoTArray<nsCSSProperty, 16> shorthandsUsed;
   for (index = 0; index < count; index++) {
     nsCSSProperty property = OrderValueAt(index);
+    if (!nsCSSProps::IsEnabled(property)) {
+      continue;
+    }
     bool doneProperty = false;
 
     // If we already used this property in a shorthand, skip it.
diff --git a/layout/style/test/test_font_feature_values_parsing.html b/layout/style/test/test_font_feature_values_parsing.html
index a5d4a683406..8fcc1b67fc9 100644
--- a/layout/style/test/test_font_feature_values_parsing.html
+++ b/layout/style/test/test_font_feature_values_parsing.html
@@ -335,6 +335,10 @@ function testOneRule(testrule) {
 }
 
 function testFontFeatureValuesRuleParsing() {
+  // Gecko-specific check - if pref not set, skip these tests
+  if (window.SpecialPowers && !window.SpecialPowers.getBoolPref("layout.css.font-features.enabled")) {
+    return;
+  }
   var i;
   for (i = 0; i < testrules.length; i++) {
     var testrule = testrules[i];
diff --git a/layout/style/test/test_specified_value_serialization.html b/layout/style/test/test_specified_value_serialization.html
index 9cc2f9b2f14..c0369d3b0a6 100644
--- a/layout/style/test/test_specified_value_serialization.html
+++ b/layout/style/test/test_specified_value_serialization.html
@@ -50,11 +50,13 @@ is(elt.style.getPropertyValue("transform"),
    "translateX(5px) translateY(10px) translateZ(2px) rotateX(30deg) rotateY(30deg) rotateZ(5deg) skewX(10deg) skewY(10deg) scaleX(2) scaleY(0.5) scaleZ(2)",
    "expected case canonicalization of transform functions");
 
-elt.setAttribute("style",
-                 "font-variant-alternates: SWASH(fOo) stYLIStiC(Bar)");
-is(elt.style.getPropertyValue("font-variant-alternates"),
-   "swash(fOo) stylistic(Bar)",
-   "expected case canonicalization of transform functions");
+if (SpecialPowers.getBoolPref("layout.css.font-features.enabled")) {
+  elt.setAttribute("style",
+                   "font-variant-alternates: SWASH(fOo) stYLIStiC(Bar)");
+  is(elt.style.getPropertyValue("font-variant-alternates"),
+     "swash(fOo) stylistic(Bar)",
+     "expected case canonicalization of transform functions");
+}
 
 elt.setAttribute("style", ""); // leave the page in a useful state