--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -134,17 +134,17 @@ 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 STICKY_ENABLED_PREF_NAME "layout.css.sticky.enabled"
 #define DISPLAY_CONTENTS_ENABLED_PREF_NAME "layout.css.display-contents.enabled"
-#define TEXT_ALIGN_TRUE_ENABLED_PREF_NAME "layout.css.text-align-true-value.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"
 
 #ifdef DEBUG
 // TODO: remove, see bug 598468.
 bool nsLayoutUtils::gPreventAssertInCompareTreePosition = false;
 #endif // DEBUG
 
 typedef FrameMetrics::ViewID ViewID;
@@ -276,30 +276,30 @@ DisplayContentsEnabledPrefChangeCallback
   // 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-true-value.enabled" changes, this
+// 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 "true" in those tables.
 static void
-TextAlignTrueEnabledPrefChangeCallback(const char* aPrefName, void* aClosure)
-{
-  NS_ASSERTION(strcmp(aPrefName, TEXT_ALIGN_TRUE_ENABLED_PREF_NAME) == 0,
-               "Did you misspell " TEXT_ALIGN_TRUE_ENABLED_PREF_NAME " ?");
+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 " ?");
 
   static bool sIsInitialized;
   static int32_t sIndexOfTrueInTextAlignTable;
   static int32_t sIndexOfTrueInTextAlignLastTable;
-  bool isTextAlignTrueEnabled =
-    Preferences::GetBool(TEXT_ALIGN_TRUE_ENABLED_PREF_NAME, false);
+  bool isTextAlignUnsafeEnabled =
+    Preferences::GetBool(TEXT_ALIGN_UNSAFE_ENABLED_PREF_NAME, false);
 
   if (!sIsInitialized) {
     // First run: find the position of "true" in kTextAlignKTable.
     sIndexOfTrueInTextAlignTable =
       nsCSSProps::FindIndexOfKeyword(eCSSKeyword_unsafe,
                                      nsCSSProps::kTextAlignKTable);
     // First run: find the position of "true" in kTextAlignLastKTable.
     sIndexOfTrueInTextAlignLastTable =
@@ -307,20 +307,20 @@ TextAlignTrueEnabledPrefChangeCallback(c
                                      nsCSSProps::kTextAlignLastKTable);
     sIsInitialized = true;
   }
 
   // OK -- now, stomp on or restore the "true" entry in the keyword tables,
   // depending on whether the pref is enabled vs. disabled.
   MOZ_ASSERT(sIndexOfTrueInTextAlignTable >= 0);
   nsCSSProps::kTextAlignKTable[sIndexOfTrueInTextAlignTable].mKeyword =
-    isTextAlignTrueEnabled ? eCSSKeyword_unsafe : eCSSKeyword_UNKNOWN;
+    isTextAlignUnsafeEnabled ? eCSSKeyword_unsafe : eCSSKeyword_UNKNOWN;
   MOZ_ASSERT(sIndexOfTrueInTextAlignLastTable >= 0);
   nsCSSProps::kTextAlignLastKTable[sIndexOfTrueInTextAlignLastTable].mKeyword =
-    isTextAlignTrueEnabled ? eCSSKeyword_unsafe : eCSSKeyword_UNKNOWN;
+    isTextAlignUnsafeEnabled ? eCSSKeyword_unsafe : eCSSKeyword_UNKNOWN;
 }
 
 // When the pref "layout.css.float-logical-values.enabled" changes, this
 // function is called to let us update kFloatKTable & kClearKTable,
 // to selectively disable or restore the entries for logical values
 // (inline-start and inline-end) in those tables.
 static void
 FloatLogicalValuesEnabledPrefChangeCallback(const char* aPrefName,
@@ -654,29 +654,29 @@ nsLayoutUtils::IsGridTemplateSubgridValu
                                  GRID_TEMPLATE_SUBGRID_ENABLED_PREF_NAME,
                                  false);
   }
 
   return sGridTemplateSubgridValueEnabled;
 }
 
 bool
-nsLayoutUtils::IsTextAlignTrueValueEnabled()
-{
-  static bool sTextAlignTrueValueEnabled;
-  static bool sTextAlignTrueValueEnabledPrefCached = false;
-
-  if (!sTextAlignTrueValueEnabledPrefCached) {
-    sTextAlignTrueValueEnabledPrefCached = true;
-    Preferences::AddBoolVarCache(&sTextAlignTrueValueEnabled,
-                                 TEXT_ALIGN_TRUE_ENABLED_PREF_NAME,
+nsLayoutUtils::IsTextAlignUnsafeValueEnabled()
+{
+  static bool sTextAlignUnsafeValueEnabled;
+  static bool sTextAlignUnsafeValueEnabledPrefCached = false;
+
+  if (!sTextAlignUnsafeValueEnabledPrefCached) {
+    sTextAlignUnsafeValueEnabledPrefCached = true;
+    Preferences::AddBoolVarCache(&sTextAlignUnsafeValueEnabled,
+                                 TEXT_ALIGN_UNSAFE_ENABLED_PREF_NAME,
                                  false);
   }
 
-  return sTextAlignTrueValueEnabled;
+  return sTextAlignUnsafeValueEnabled;
 }
 
 void
 nsLayoutUtils::UnionChildOverflow(nsIFrame* aFrame,
                                   nsOverflowAreas& aOverflowAreas,
                                   FrameChildListIDs aSkipChildLists)
 {
   // Iterate over all children except pop-ups.
@@ -7533,24 +7533,24 @@ nsLayoutUtils::Initialize()
                                "svg.transform-box.enabled");
 
   Preferences::RegisterCallback(GridEnabledPrefChangeCallback,
                                 GRID_ENABLED_PREF_NAME);
   GridEnabledPrefChangeCallback(GRID_ENABLED_PREF_NAME, nullptr);
   Preferences::RegisterCallback(StickyEnabledPrefChangeCallback,
                                 STICKY_ENABLED_PREF_NAME);
   StickyEnabledPrefChangeCallback(STICKY_ENABLED_PREF_NAME, nullptr);
-  Preferences::RegisterCallback(TextAlignTrueEnabledPrefChangeCallback,
-                                TEXT_ALIGN_TRUE_ENABLED_PREF_NAME);
+  Preferences::RegisterCallback(TextAlignUnsafeEnabledPrefChangeCallback,
+                                TEXT_ALIGN_UNSAFE_ENABLED_PREF_NAME);
   Preferences::RegisterCallback(DisplayContentsEnabledPrefChangeCallback,
                                 DISPLAY_CONTENTS_ENABLED_PREF_NAME);
   DisplayContentsEnabledPrefChangeCallback(DISPLAY_CONTENTS_ENABLED_PREF_NAME,
                                            nullptr);
-  TextAlignTrueEnabledPrefChangeCallback(TEXT_ALIGN_TRUE_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);
 
   nsComputedDOMStyle::RegisterPrefChangeCallbacks();
 }
 

--- a/layout/base/nsLayoutUtils.h
+++ b/layout/base/nsLayoutUtils.h
@@ -2286,17 +2286,17 @@ public:
    * value is enabled.
    */
   static bool IsGridTemplateSubgridValueEnabled();
 
   /**
    * Checks whether support for the CSS text-align (and -moz-text-align-last)
    * 'true' value is enabled.
    */
-  static bool IsTextAlignTrueValueEnabled();
+  static bool IsTextAlignUnsafeValueEnabled();
 
   /**
    * Checks if CSS variables are currently enabled.
    */
   static bool CSSVariablesEnabled()
   {
     return sCSSVariablesEnabled;
   }

--- a/layout/reftests/text/reftest.list
+++ b/layout/reftests/text/reftest.list
@@ -302,17 +302,17 @@ HTTP(..) == graphite-bidi-1.html graphit
 
 == auto-hyphenation-transformed-1.html auto-hyphenation-transformed-1-ref.html
 
 # osx-font-smoothing - with and without subpixel AA, only under OSX
 fails-if(!cocoaWidget||OSX==1006||OSX==1007) != osx-font-smoothing.html osx-font-smoothing-ref.html
 fails-if(!cocoaWidget||OSX==1006||OSX==1007) != osx-font-smoothing-2.html osx-font-smoothing-2-notref.html
 == osx-font-smoothing-2.html osx-font-smoothing-2-ref.html
 
-pref(layout.css.text-align-true-value.enabled,true) == text-align-true.html text-align-true-ref.html
+pref(layout.css.text-align-unsafe-value.enabled,true) == text-align-true.html text-align-true-ref.html
 
 # stray control chars should be visible by default, bug 1099557
 != control-chars-01a.html control-chars-01-notref.html
 != control-chars-01b.html control-chars-01-notref.html
 != control-chars-01c.html control-chars-01-notref.html
 != control-chars-01d.html control-chars-01-notref.html
 != control-chars-02.html control-chars-02-notref.html
 == control-chars-03a.html control-chars-03-ref.html

--- a/layout/style/nsCSSParser.cpp
+++ b/layout/style/nsCSSParser.cpp
@@ -14882,17 +14882,17 @@ CSSParserImpl::ParseTextAlign(nsCSSValue
     return true;
   }
 
   nsCSSValue left;
   if (!ParseSingleTokenVariant(left, VARIANT_KEYWORD, aTable)) {
     return false;
   }
 
-  if (!nsLayoutUtils::IsTextAlignTrueValueEnabled()) {
+  if (!nsLayoutUtils::IsTextAlignUnsafeValueEnabled()) {
     aValue = left;
     return true;
   }
 
   nsCSSValue right;
   if (ParseSingleTokenVariant(right, VARIANT_KEYWORD, aTable)) {
     // 'true' must be combined with some other value than 'true'.
     if (left.GetIntValue() == NS_STYLE_TEXT_ALIGN_UNSAFE &&

--- a/layout/style/nsCSSProps.h
+++ b/layout/style/nsCSSProps.h
@@ -808,17 +808,17 @@ public:
   static const KTableEntry kSpeakKTable[];
   static const KTableEntry kSpeakHeaderKTable[];
   static const KTableEntry kSpeakNumeralKTable[];
   static const KTableEntry kSpeakPunctuationKTable[];
   static const KTableEntry kSpeechRateKTable[];
   static const KTableEntry kStackSizingKTable[];
   static const KTableEntry kTableLayoutKTable[];
   // Not const because we modify its entries when the pref
-  // "layout.css.text-align-true-value.enabled" changes:
+  // "layout.css.text-align-unsafe-value.enabled" changes:
   static KTableEntry kTextAlignKTable[];
   static KTableEntry kTextAlignLastKTable[];
   static const KTableEntry kTextCombineUprightKTable[];
   static const KTableEntry kTextDecorationLineKTable[];
   static const KTableEntry kTextDecorationStyleKTable[];
   static const KTableEntry kTextEmphasisPositionKTable[];
   static const KTableEntry kTextEmphasisStyleFillKTable[];
   static const KTableEntry kTextEmphasisStyleShapeKTable[];

--- a/layout/style/test/property_database.js
+++ b/layout/style/test/property_database.js
@@ -7295,17 +7295,17 @@ if (IsCSSPropertyPrefEnabled("layout.css
   gCSSProperties["box-shadow"].invalid_values.push("unset, 2px 2px", "2px 2px, unset", "inset unset");
   gCSSProperties["text-overflow"].invalid_values.push('"hello" unset', 'unset "hello"', 'clip unset', 'unset clip', 'unset inherit', 'unset none', 'initial unset');
   gCSSProperties["text-shadow"].invalid_values.push("unset, 2px 2px", "2px 2px, unset");
   gCSSProperties["transition"].invalid_values.push("2s unset");
   gCSSProperties["transition-property"].invalid_values.push("unset, color", "color, unset");
   if (IsCSSPropertyPrefEnabled("layout.css.filters.enabled")) {
     gCSSProperties["filter"].invalid_values.push("drop-shadow(unset, 2px 2px)", "drop-shadow(2px 2px, unset)");
   }
-  if (IsCSSPropertyPrefEnabled("layout.css.text-align-true-value.enabled")) {
+  if (IsCSSPropertyPrefEnabled("layout.css.text-align-unsafe-value.enabled")) {
     gCSSProperties["text-align"].other_values.push("true left");
   } else {
     gCSSProperties["text-align"].invalid_values.push("true left");
   }
 }
 
 if (IsCSSPropertyPrefEnabled("layout.css.float-logical-values.enabled")) {
   gCSSProperties["float"].other_values.push("inline-start");

--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -2342,17 +2342,17 @@ pref("layout.css.getBoxQuads.enabled", t
 // Is support for GeometryUtils.convert*FromNode enabled?
 #ifdef RELEASE_BUILD
 pref("layout.css.convertFromNode.enabled", false);
 #else
 pref("layout.css.convertFromNode.enabled", true);
 #endif
 
 // Is support for CSS "text-align: true X" enabled?
-pref("layout.css.text-align-true-value.enabled", false);
+pref("layout.css.text-align-unsafe-value.enabled", false);
 
 // Is support for CSS "float: inline-{start,end}" and
 // "clear: inline-{start,end}" enabled?
 #if defined(MOZ_B2G) || defined(NIGHTLY_BUILD)
 pref("layout.css.float-logical-values.enabled", true);
 #else
 pref("layout.css.float-logical-values.enabled", false);
 #endif