--- a/layout/style/nsComputedDOMStyle.cpp
+++ b/layout/style/nsComputedDOMStyle.cpp
@@ -7,16 +7,17 @@
 /* DOM object returned from element.getComputedStyle() */
 
 #include "nsComputedDOMStyle.h"
 
 #include "mozilla/ArrayUtils.h"
 #include "mozilla/FloatingPoint.h"
 #include "mozilla/FontPropertyTypes.h"
 #include "mozilla/Preferences.h"
+#include "mozilla/StaticPtr.h"
 
 #include "nsError.h"
 #include "nsIFrame.h"
 #include "nsIFrameInlines.h"
 #include "mozilla/ComputedStyle.h"
 #include "nsIScrollableFrame.h"
 #include "nsContentUtils.h"
 #include "nsIContent.h"
@@ -5487,34 +5488,47 @@ nsComputedDOMStyle::ParentChainChanged(n
 
 /* static */ ComputedStyleMap*
 nsComputedDOMStyle::GetComputedStyleMap()
 {
   static ComputedStyleMap map{};
   return ↦
 }
 
+static StaticAutoPtr<nsTArray<const char*>> gCallbackPrefs;
+
 /* static */ void
 nsComputedDOMStyle::RegisterPrefChangeCallbacks()
 {
   // Note that this will register callbacks for all properties with prefs, not
   // just those that are implemented on computed style objects, as it's not
   // easy to grab specific property data from ServoCSSPropList.h based on the
   // entries iterated in nsComputedDOMStylePropertyList.h.
-  ComputedStyleMap* data = GetComputedStyleMap();
+
+  AutoTArray<const char*, 64> prefs;
   for (const auto* p = nsCSSProps::kPropertyPrefTable;
        p->mPropID != eCSSProperty_UNKNOWN; p++) {
-    nsCString name;
-    name.AssignLiteral(p->mPref, strlen(p->mPref));
-    Preferences::RegisterCallback(MarkComputedStyleMapDirty, name, data);
-  }
+    // Many properties are controlled by the same preference, so de-duplicate
+    // them before adding observers.
+    if (!prefs.ContainsSorted(p->mPref)) {
+      prefs.InsertElementSorted(p->mPref);
+    }
+  }
+  prefs.AppendElement(nullptr);
+
+  MOZ_ASSERT(!gCallbackPrefs);
+  gCallbackPrefs = new nsTArray<const char*>(std::move(prefs));
+
+  Preferences::RegisterCallbacks(MarkComputedStyleMapDirty,
+                                 gCallbackPrefs->Elements(),
+                                 GetComputedStyleMap());
 }
 
 /* static */ void
 nsComputedDOMStyle::UnregisterPrefChangeCallbacks()
 {
-  ComputedStyleMap* data = GetComputedStyleMap();
-  for (const auto* p = nsCSSProps::kPropertyPrefTable;
-       p->mPropID != eCSSProperty_UNKNOWN; p++) {
-    Preferences::UnregisterCallback(MarkComputedStyleMapDirty,
-                                    nsDependentCString(p->mPref), data);
-  }
-}
+  MOZ_ASSERT(gCallbackPrefs);
+
+  Preferences::UnregisterCallbacks(MarkComputedStyleMapDirty,
+                                   gCallbackPrefs->Elements(),
+                                   GetComputedStyleMap());
+  gCallbackPrefs = nullptr;
+}