diff --git a/dom/ipc/ContentParent.cpp b/dom/ipc/ContentParent.cpp
index 50e86857b5a6..0dcf04ec9eb8 100644
--- a/dom/ipc/ContentParent.cpp
+++ b/dom/ipc/ContentParent.cpp
@@ -79,7 +79,6 @@
 #include "mozilla/Components.h"
 #include "mozilla/Sprintf.h"
 #include "mozilla/StaticPrefs_dom.h"
-#include "mozilla/StaticPrefs_fission.h"
 #include "mozilla/StaticPrefs_media.h"
 #include "mozilla/StaticPrefs_widget.h"
 #include "mozilla/StyleSheet.h"
@@ -648,23 +647,6 @@ static const char* sObserverTopics[] = {
     "network:socket-process-crashed",
 };
 
-static const char kFissionEnforceBlockList[] =
-    "fission.enforceBlocklistedPrefsInSubprocesses";
-static const char kFissionOmitBlockListValues[] =
-    "fission.omitBlocklistedPrefsInSubprocesses";
-
-static void OnFissionBlocklistPrefChange(const char* aPref, void* aData) {
-  if (strcmp(aPref, kFissionEnforceBlockList) == 0) {
-    sCrashOnBlocklistedPref =
-        StaticPrefs::fission_enforceBlocklistedPrefsInSubprocesses();
-  } else if (strcmp(aPref, kFissionOmitBlockListValues) == 0) {
-    sOmitBlocklistedPrefValues =
-        StaticPrefs::fission_omitBlocklistedPrefsInSubprocesses();
-  } else {
-    MOZ_CRASH("Unknown pref passed to callback");
-  }
-}
-
 // PreallocateProcess is called by the PreallocatedProcessManager.
 // ContentParent then takes this process back within GetNewOrUsedBrowserProcess.
 /*static*/ already_AddRefed<ContentParent>
@@ -694,11 +676,6 @@ void ContentParent::StartUp() {
   BackgroundChild::Startup();
   ClientManager::Startup();
 
-  Preferences::RegisterCallbackAndCall(&OnFissionBlocklistPrefChange,
-                                       kFissionEnforceBlockList);
-  Preferences::RegisterCallbackAndCall(&OnFissionBlocklistPrefChange,
-                                       kFissionOmitBlockListValues);
-
 #if defined(XP_LINUX) && defined(MOZ_SANDBOX)
   sSandboxBrokerPolicyFactory = MakeUnique<SandboxBrokerPolicyFactory>();
 #endif
@@ -2532,9 +2509,9 @@ bool ContentParent::BeginSubprocessLaunch(ProcessPriority aPriority) {
 
   // Instantiate the pref serializer. It will be cleaned up in
   // `LaunchSubprocessReject`/`LaunchSubprocessResolve`.
-  mPrefSerializer = MakeUnique<mozilla::ipc::SharedPreferenceSerializer>();
-  if (!mPrefSerializer->SerializeToSharedMemory(GeckoProcessType_Content,
-                                                GetRemoteType())) {
+  mPrefSerializer = MakeUnique<mozilla::ipc::SharedPreferenceSerializer>(
+      ShouldSyncPreference);
+  if (!mPrefSerializer->SerializeToSharedMemory()) {
     NS_WARNING("SharedPreferenceSerializer::SerializeToSharedMemory failed");
     MarkAsDead();
     return false;
@@ -3655,11 +3632,13 @@ ContentParent::Observe(nsISupports* aSubject, const char* aTopic,
     // We know prefs are ASCII here.
     NS_LossyConvertUTF16toASCII strData(aData);
 
-    Pref pref(strData, /* isLocked */ false,
-              /* isSanitized */ false, Nothing(), Nothing());
+    // A pref changed. If it is useful to do so, inform child processes.
+    if (!ShouldSyncPreference(strData.Data())) {
+      return NS_OK;
+    }
 
-    Preferences::GetPreference(&pref, GeckoProcessType_Content,
-                               GetRemoteType());
+    Pref pref(strData, /* isLocked */ false, Nothing(), Nothing());
+    Preferences::GetPreference(&pref);
     if (IsInitialized()) {
       MOZ_ASSERT(mQueuedPrefs.IsEmpty());
       if (!SendPreferenceUpdate(pref)) {
@@ -3806,6 +3785,37 @@ ContentParent::Observe(nsISupports* aSubject, const char* aTopic,
   return NS_OK;
 }
 
+/* static */
+bool ContentParent::ShouldSyncPreference(const char* aPref) {
+#define PARENT_ONLY_PREF_LIST_ENTRY(s) \
+  { s, (sizeof(s) / sizeof(char)) - 1 }
+  struct ParentOnlyPrefListEntry {
+    const char* mPrefBranch;
+    size_t mLen;
+  };
+  // These prefs are not useful in child processes.
+  static const ParentOnlyPrefListEntry sParentOnlyPrefBranchList[] = {
+      PARENT_ONLY_PREF_LIST_ENTRY("app.update.lastUpdateTime."),
+      PARENT_ONLY_PREF_LIST_ENTRY("datareporting.policy."),
+      PARENT_ONLY_PREF_LIST_ENTRY("browser.safebrowsing.provider."),
+      PARENT_ONLY_PREF_LIST_ENTRY("browser.shell."),
+      PARENT_ONLY_PREF_LIST_ENTRY("browser.slowStartup."),
+      PARENT_ONLY_PREF_LIST_ENTRY("browser.startup."),
+      PARENT_ONLY_PREF_LIST_ENTRY("extensions.getAddons.cache."),
+      PARENT_ONLY_PREF_LIST_ENTRY("media.gmp-manager."),
+      PARENT_ONLY_PREF_LIST_ENTRY("media.gmp-gmpopenh264."),
+      PARENT_ONLY_PREF_LIST_ENTRY("privacy.sanitize."),
+  };
+#undef PARENT_ONLY_PREF_LIST_ENTRY
+
+  for (const auto& entry : sParentOnlyPrefBranchList) {
+    if (strncmp(entry.mPrefBranch, aPref, entry.mLen) == 0) {
+      return false;
+    }
+  }
+  return true;
+}
+
 void ContentParent::UpdateNetworkLinkType() {
   nsresult rv;
   nsCOMPtr<nsINetworkLinkService> nls =
diff --git a/dom/ipc/ContentParent.h b/dom/ipc/ContentParent.h
index a63419ed37de..b6276ef19df0 100644
--- a/dom/ipc/ContentParent.h
+++ b/dom/ipc/ContentParent.h
@@ -1460,6 +1460,8 @@ class ContentParent final
 
   void UpdateNetworkLinkType();
 
+  static bool ShouldSyncPreference(const char* aPref);
+
   already_AddRefed<JSActor> InitJSActor(JS::HandleObject aMaybeActor,
                                         const nsACString& aName,
                                         ErrorResult& aRv) override;
diff --git a/dom/ipc/PrefsTypes.ipdlh b/dom/ipc/PrefsTypes.ipdlh
index 403c7aaf4296..762351a42921 100644
--- a/dom/ipc/PrefsTypes.ipdlh
+++ b/dom/ipc/PrefsTypes.ipdlh
@@ -23,7 +23,6 @@ union PrefValue {
 struct Pref {
   nsCString name;
   bool isLocked;
-  bool isSanitized;
   PrefValue? defaultValue;
   PrefValue? userValue;
 };
diff --git a/dom/media/ipc/RDDProcessHost.cpp b/dom/media/ipc/RDDProcessHost.cpp
index bba6d7a4ca52..c3cff03123bd 100644
--- a/dom/media/ipc/RDDProcessHost.cpp
+++ b/dom/media/ipc/RDDProcessHost.cpp
@@ -46,9 +46,9 @@ bool RDDProcessHost::Launch(StringVector aExtraOpts) {
   MOZ_ASSERT(mLaunchPhase == LaunchPhase::Unlaunched);
   MOZ_ASSERT(!mRDDChild);
 
-  mPrefSerializer = MakeUnique<ipc::SharedPreferenceSerializer>();
-  if (!mPrefSerializer->SerializeToSharedMemory(GeckoProcessType_RDD,
-                                                /* remoteType */ ""_ns)) {
+  mPrefSerializer = MakeUnique<ipc::SharedPreferenceSerializer>(
+      dom::ContentParent::ShouldSyncPreference);
+  if (!mPrefSerializer->SerializeToSharedMemory()) {
     return false;
   }
   mPrefSerializer->AddSharedPrefCmdLineArgs(*this, aExtraOpts);
diff --git a/dom/media/ipc/RDDProcessManager.cpp b/dom/media/ipc/RDDProcessManager.cpp
index 8a6dff85dc2c..c69d9fa67824 100644
--- a/dom/media/ipc/RDDProcessManager.cpp
+++ b/dom/media/ipc/RDDProcessManager.cpp
@@ -96,11 +96,13 @@ void RDDProcessManager::OnPreferenceChange(const char16_t* aData) {
   // We know prefs are ASCII here.
   NS_LossyConvertUTF16toASCII strData(aData);
 
-  mozilla::dom::Pref pref(strData, /* isLocked */ false,
-                          /* isSanitized */ false, Nothing(), Nothing());
+  // A pref changed. If it is useful to do so, inform child processes.
+  if (!dom::ContentParent::ShouldSyncPreference(strData.Data())) {
+    return;
+  }
 
-  Preferences::GetPreference(&pref, GeckoProcessType_RDD,
-                             /* remoteType */ ""_ns);
+  mozilla::dom::Pref pref(strData, /* isLocked */ false, Nothing(), Nothing());
+  Preferences::GetPreference(&pref);
   if (!!mRDDChild) {
     MOZ_ASSERT(mQueuedPrefs.IsEmpty());
     mRDDChild->SendPreferenceUpdate(pref);
diff --git a/gfx/ipc/GPUProcessHost.cpp b/gfx/ipc/GPUProcessHost.cpp
index 7205bc3e05bf..69e79c8b98ce 100644
--- a/gfx/ipc/GPUProcessHost.cpp
+++ b/gfx/ipc/GPUProcessHost.cpp
@@ -42,9 +42,9 @@ bool GPUProcessHost::Launch(StringVector aExtraOpts) {
   MOZ_ASSERT(!mGPUChild);
   MOZ_ASSERT(!gfxPlatform::IsHeadless());
 
-  mPrefSerializer = MakeUnique<ipc::SharedPreferenceSerializer>();
-  if (!mPrefSerializer->SerializeToSharedMemory(GeckoProcessType_GPU,
-                                                /* remoteType */ ""_ns)) {
+  mPrefSerializer = MakeUnique<ipc::SharedPreferenceSerializer>(
+      dom::ContentParent::ShouldSyncPreference);
+  if (!mPrefSerializer->SerializeToSharedMemory()) {
     return false;
   }
   mPrefSerializer->AddSharedPrefCmdLineArgs(*this, aExtraOpts);
diff --git a/gfx/ipc/GPUProcessManager.cpp b/gfx/ipc/GPUProcessManager.cpp
index 2d9c4798e794..ac6c627a585c 100644
--- a/gfx/ipc/GPUProcessManager.cpp
+++ b/gfx/ipc/GPUProcessManager.cpp
@@ -163,11 +163,13 @@ void GPUProcessManager::OnPreferenceChange(const char16_t* aData) {
   // We know prefs are ASCII here.
   NS_LossyConvertUTF16toASCII strData(aData);
 
-  mozilla::dom::Pref pref(strData, /* isLocked */ false,
-                          /* isSanitized */ false, Nothing(), Nothing());
+  // A pref changed. If it is useful to do so, inform child processes.
+  if (!dom::ContentParent::ShouldSyncPreference(strData.Data())) {
+    return;
+  }
 
-  Preferences::GetPreference(&pref, GeckoProcessType_GPU,
-                             /* remoteType */ ""_ns);
+  mozilla::dom::Pref pref(strData, /* isLocked */ false, Nothing(), Nothing());
+  Preferences::GetPreference(&pref);
   if (!!mGPUChild) {
     MOZ_ASSERT(mQueuedPrefs.IsEmpty());
     mGPUChild->SendPreferenceUpdate(pref);
diff --git a/gfx/vr/ipc/VRProcessManager.cpp b/gfx/vr/ipc/VRProcessManager.cpp
index f3bc13bac03b..01f56b3648a3 100644
--- a/gfx/vr/ipc/VRProcessManager.cpp
+++ b/gfx/vr/ipc/VRProcessManager.cpp
@@ -216,11 +216,13 @@ void VRProcessManager::OnPreferenceChange(const char16_t* aData) {
   // We know prefs are ASCII here.
   NS_LossyConvertUTF16toASCII strData(aData);
 
-  mozilla::dom::Pref pref(strData, /* isLocked */ false,
-                          /* isSanitized */ false, Nothing(), Nothing());
+  // A pref changed. If it is useful to do so, inform child processes.
+  if (!dom::ContentParent::ShouldSyncPreference(strData.Data())) {
+    return;
+  }
 
-  Preferences::GetPreference(&pref, GeckoProcessType_VR,
-                             /* remoteType */ ""_ns);
+  mozilla::dom::Pref pref(strData, /* isLocked */ false, Nothing(), Nothing());
+  Preferences::GetPreference(&pref);
   if (!!mVRChild) {
     MOZ_ASSERT(mQueuedPrefs.IsEmpty());
     mVRChild->SendPreferenceUpdate(pref);
diff --git a/gfx/vr/ipc/VRProcessParent.cpp b/gfx/vr/ipc/VRProcessParent.cpp
index 2546c0d31171..37187bb57693 100644
--- a/gfx/vr/ipc/VRProcessParent.cpp
+++ b/gfx/vr/ipc/VRProcessParent.cpp
@@ -16,7 +16,6 @@
 #include "mozilla/ipc/ProcessUtils.h"
 #include "mozilla/ipc/ProtocolTypes.h"
 #include "mozilla/ipc/ProtocolUtils.h"  // for IToplevelProtocol
-#include "mozilla/Preferences.h"
 #include "mozilla/StaticPrefs_dom.h"
 #include "mozilla/TimeStamp.h"  // for TimeStamp
 #include "mozilla/Unused.h"
@@ -55,9 +54,9 @@ bool VRProcessParent::Launch() {
   std::vector<std::string> extraArgs;
   ProcessChild::AddPlatformBuildID(extraArgs);
 
-  mPrefSerializer = MakeUnique<ipc::SharedPreferenceSerializer>();
-  if (!mPrefSerializer->SerializeToSharedMemory(GeckoProcessType_VR,
-                                                /* remoteType */ ""_ns)) {
+  mPrefSerializer = MakeUnique<ipc::SharedPreferenceSerializer>(
+      dom::ContentParent::ShouldSyncPreference);
+  if (!mPrefSerializer->SerializeToSharedMemory()) {
     return false;
   }
   mPrefSerializer->AddSharedPrefCmdLineArgs(*this, extraArgs);
diff --git a/ipc/glue/ProcessUtils.h b/ipc/glue/ProcessUtils.h
index b0f146ef6d4a..023750847f82 100644
--- a/ipc/glue/ProcessUtils.h
+++ b/ipc/glue/ProcessUtils.h
@@ -13,8 +13,6 @@
 #include "mozilla/ipc/FileDescriptor.h"
 #include "base/shared_memory.h"
 #include "mozilla/Maybe.h"
-#include "mozilla/Preferences.h"
-#include "nsXULAppAPI.h"
 
 namespace mozilla {
 namespace ipc {
@@ -27,12 +25,12 @@ void SetThisProcessName(const char* aName);
 
 class SharedPreferenceSerializer final {
  public:
-  explicit SharedPreferenceSerializer();
+  explicit SharedPreferenceSerializer(
+      std::function<bool(const char*)>&& aShouldSerializeFn);
   SharedPreferenceSerializer(SharedPreferenceSerializer&& aOther);
   ~SharedPreferenceSerializer();
 
-  bool SerializeToSharedMemory(const GeckoProcessType aDestinationProcessType,
-                               const nsACString& aDestinationRemoteType);
+  bool SerializeToSharedMemory();
 
   size_t GetPrefMapSize() const { return mPrefMapSize; }
   size_t GetPrefsLength() const { return mPrefsLength; }
@@ -50,6 +48,7 @@ class SharedPreferenceSerializer final {
   size_t mPrefsLength;
   UniqueFileHandle mPrefMapHandle;
   UniqueFileHandle mPrefsHandle;
+  std::function<bool(const char*)> mShouldSerializeFn;
 };
 
 class SharedPreferenceDeserializer final {
diff --git a/ipc/glue/ProcessUtils_common.cpp b/ipc/glue/ProcessUtils_common.cpp
index 69eb4bdf287f..5dbe13cc7b2f 100644
--- a/ipc/glue/ProcessUtils_common.cpp
+++ b/ipc/glue/ProcessUtils_common.cpp
@@ -8,7 +8,6 @@
 
 #include "mozilla/Preferences.h"
 #include "mozilla/GeckoArgs.h"
-#include "mozilla/dom/RemoteType.h"
 #include "mozilla/ipc/GeckoChildProcessHost.h"
 #include "mozilla/UniquePtrExtensions.h"
 #include "nsPrintfCString.h"
@@ -18,8 +17,9 @@
 namespace mozilla {
 namespace ipc {
 
-SharedPreferenceSerializer::SharedPreferenceSerializer()
-    : mPrefMapSize(0), mPrefsLength(0) {
+SharedPreferenceSerializer::SharedPreferenceSerializer(
+    std::function<bool(const char*)>&& aShouldSerializeFn)
+    : mPrefMapSize(0), mPrefsLength(0), mShouldSerializeFn(aShouldSerializeFn) {
   MOZ_COUNT_CTOR(SharedPreferenceSerializer);
 }
 
@@ -36,20 +36,13 @@ SharedPreferenceSerializer::SharedPreferenceSerializer(
   MOZ_COUNT_CTOR(SharedPreferenceSerializer);
 }
 
-bool SharedPreferenceSerializer::SerializeToSharedMemory(
-    const GeckoProcessType aDestinationProcessType,
-    const nsACString& aDestinationRemoteType) {
+bool SharedPreferenceSerializer::SerializeToSharedMemory() {
   mPrefMapHandle =
       Preferences::EnsureSnapshot(&mPrefMapSize).TakePlatformHandle();
 
-  bool destIsWebContent =
-      aDestinationProcessType == GeckoProcessType_Content &&
-      (StringBeginsWith(aDestinationRemoteType, WEB_REMOTE_TYPE) ||
-       StringBeginsWith(aDestinationRemoteType, PREALLOC_REMOTE_TYPE));
-
   // Serialize the early prefs.
   nsAutoCStringN<1024> prefs;
-  Preferences::SerializePreferences(prefs, destIsWebContent);
+  Preferences::SerializePreferences(prefs, mShouldSerializeFn);
   mPrefsLength = prefs.Length();
 
   base::SharedMemory shm;
diff --git a/ipc/glue/UtilityProcessHost.cpp b/ipc/glue/UtilityProcessHost.cpp
index 2f95d4eb56a0..45e7e59f02d6 100644
--- a/ipc/glue/UtilityProcessHost.cpp
+++ b/ipc/glue/UtilityProcessHost.cpp
@@ -60,9 +60,9 @@ bool UtilityProcessHost::Launch(StringVector aExtraOpts) {
   MOZ_ASSERT(mLaunchPhase == LaunchPhase::Unlaunched);
   MOZ_ASSERT(!mUtilityProcessParent);
 
-  mPrefSerializer = MakeUnique<ipc::SharedPreferenceSerializer>();
-  if (!mPrefSerializer->SerializeToSharedMemory(GeckoProcessType_Utility,
-                                                /* remoteType */ ""_ns)) {
+  mPrefSerializer = MakeUnique<ipc::SharedPreferenceSerializer>(
+      dom::ContentParent::ShouldSyncPreference);
+  if (!mPrefSerializer->SerializeToSharedMemory()) {
     return false;
   }
   mPrefSerializer->AddSharedPrefCmdLineArgs(*this, aExtraOpts);
diff --git a/ipc/glue/UtilityProcessManager.cpp b/ipc/glue/UtilityProcessManager.cpp
index 040702b97aa6..c52c6e6328bc 100644
--- a/ipc/glue/UtilityProcessManager.cpp
+++ b/ipc/glue/UtilityProcessManager.cpp
@@ -94,10 +94,13 @@ void UtilityProcessManager::OnPreferenceChange(const char16_t* aData) {
   // We know prefs are ASCII here.
   NS_LossyConvertUTF16toASCII strData(aData);
 
-  mozilla::dom::Pref pref(strData, /* isLocked */ false,
-                          /* isSanitized */ false, Nothing(), Nothing());
-  Preferences::GetPreference(&pref, GeckoProcessType_Utility,
-                             /* remoteType */ ""_ns);
+  // A pref changed. If it is useful to do so, inform child processes.
+  if (!dom::ContentParent::ShouldSyncPreference(strData.Data())) {
+    return;
+  }
+
+  mozilla::dom::Pref pref(strData, /* isLocked */ false, Nothing(), Nothing());
+  Preferences::GetPreference(&pref);
 
   for (auto& p : mProcesses) {
     if (!p) {
diff --git a/ipc/ipdl/test/gtest/IPDLUnitTest.cpp b/ipc/ipdl/test/gtest/IPDLUnitTest.cpp
index 9e586d3305f2..4eab8031c3f2 100644
--- a/ipc/ipdl/test/gtest/IPDLUnitTest.cpp
+++ b/ipc/ipdl/test/gtest/IPDLUnitTest.cpp
@@ -49,9 +49,9 @@ already_AddRefed<IPDLUnitTestParent> IPDLUnitTestParent::CreateCrossProcess() {
 
   std::vector<std::string> extraArgs;
 
-  auto prefSerializer = MakeUnique<ipc::SharedPreferenceSerializer>();
-  if (!prefSerializer->SerializeToSharedMemory(GeckoProcessType_IPDLUnitTest,
-                                               /* remoteType */ ""_ns)) {
+  auto prefSerializer = MakeUnique<ipc::SharedPreferenceSerializer>(
+      mozilla::dom::ContentParent::ShouldSyncPreference);
+  if (!prefSerializer->SerializeToSharedMemory()) {
     ADD_FAILURE()
         << "SharedPreferenceSerializer::SerializeToSharedMemory failed";
     return nullptr;
diff --git a/modules/libpref/Preferences.cpp b/modules/libpref/Preferences.cpp
index b51a45193006..1c1a8648f0c7 100644
--- a/modules/libpref/Preferences.cpp
+++ b/modules/libpref/Preferences.cpp
@@ -21,7 +21,6 @@
 #include "mozilla/Attributes.h"
 #include "mozilla/Components.h"
 #include "mozilla/dom/PContent.h"
-#include "mozilla/dom/RemoteType.h"
 #include "mozilla/HashFunctions.h"
 #include "mozilla/HashTable.h"
 #include "mozilla/Logging.h"
@@ -428,28 +427,17 @@ struct PrefsSizes {
 
 static StaticRefPtr<SharedPrefMap> gSharedMap;
 
-// Arena for Pref names.
-// Never access sPrefNameArena directly, always use PrefNameArena()
-// because it must only be accessed on the Main Thread
-typedef ArenaAllocator<4096, 1> NameArena;
-static NameArena* sPrefNameArena;
-
-static inline NameArena& PrefNameArena() {
+// Arena for Pref names. Inside a function so we can assert it's only accessed
+// on the main thread.
+static inline ArenaAllocator<4096, 1>& PrefNameArena() {
   MOZ_ASSERT(NS_IsMainThread());
 
-  if (!sPrefNameArena) {
-    sPrefNameArena = new NameArena();
-  }
-  return *sPrefNameArena;
+  static ArenaAllocator<4096, 1> sPrefNameArena;
+  return sPrefNameArena;
 }
 
 class PrefWrapper;
 
-// Two forward declarations for immediately below
-class Pref;
-static bool ShouldSanitizePreference(const Pref* const aPref,
-                                     bool aIsWebContentProcess = true);
-
 class Pref {
  public:
   explicit Pref(const nsACString& aName)
@@ -457,7 +445,6 @@ class Pref {
         mType(static_cast<uint32_t>(PrefType::None)),
         mIsSticky(false),
         mIsLocked(false),
-        mIsSanitized(false),
         mHasDefaultValue(false),
         mHasUserValue(false),
         mIsSkippedByIteration(false),
@@ -495,18 +482,14 @@ class Pref {
 
   bool IsSticky() const { return mIsSticky; }
 
-  bool IsSanitized() const { return mIsSanitized; }
-
   bool HasDefaultValue() const { return mHasDefaultValue; }
   bool HasUserValue() const { return mHasUserValue; }
 
   template <typename T>
   void AddToMap(SharedPrefMapBuilder& aMap) {
-    // Sanitized preferences should never be added to the shared pref map
-    MOZ_ASSERT(!ShouldSanitizePreference(this, true));
     aMap.Add(NameString(),
              {HasDefaultValue(), HasUserValue(), IsSticky(), IsLocked(),
-              /* isSanitized */ false, IsSkippedByIteration()},
+              IsSkippedByIteration()},
              HasDefaultValue() ? mDefaultValue.Get<T>() : T(),
              HasUserValue() ? mUserValue.Get<T>() : T());
   }
@@ -530,13 +513,6 @@ class Pref {
     MOZ_ASSERT(aKind == PrefValueKind::Default ? HasDefaultValue()
                                                : HasUserValue());
 
-    if (!XRE_IsParentProcess() && sCrashOnBlocklistedPref &&
-        ShouldSanitizePreference(this, XRE_IsContentProcess())) {
-      MOZ_CRASH_UNSAFE_PRINTF(
-          "Should not access the preference '%s' in the Content Processes",
-          Name());
-    }
-
     return aKind == PrefValueKind::Default ? mDefaultValue.mBoolVal
                                            : mUserValue.mBoolVal;
   }
@@ -546,13 +522,6 @@ class Pref {
     MOZ_ASSERT(aKind == PrefValueKind::Default ? HasDefaultValue()
                                                : HasUserValue());
 
-    if (!XRE_IsParentProcess() && sCrashOnBlocklistedPref &&
-        ShouldSanitizePreference(this, XRE_IsContentProcess())) {
-      MOZ_CRASH_UNSAFE_PRINTF(
-          "Should not access the preference '%s' in the Content Processes",
-          Name());
-    }
-
     return aKind == PrefValueKind::Default ? mDefaultValue.mIntVal
                                            : mUserValue.mIntVal;
   }
@@ -563,13 +532,6 @@ class Pref {
     MOZ_ASSERT(aKind == PrefValueKind::Default ? HasDefaultValue()
                                                : HasUserValue());
 
-    if (!XRE_IsParentProcess() && sCrashOnBlocklistedPref &&
-        ShouldSanitizePreference(this, XRE_IsContentProcess())) {
-      MOZ_CRASH_UNSAFE_PRINTF(
-          "Should not access the preference '%s' in the Content Processes",
-          Name());
-    }
-
     return aKind == PrefValueKind::Default ? mDefaultValue.mStringVal
                                            : mUserValue.mStringVal;
   }
@@ -579,16 +541,13 @@ class Pref {
     return nsDependentCString(GetBareStringValue(aKind));
   }
 
-  void ToDomPref(dom::Pref* aDomPref, bool aIsDestinationContentProcess) {
+  void ToDomPref(dom::Pref* aDomPref) {
     MOZ_ASSERT(XRE_IsParentProcess());
 
     aDomPref->name() = mName;
 
     aDomPref->isLocked() = mIsLocked;
 
-    aDomPref->isSanitized() =
-        ShouldSanitizePreference(this, aIsDestinationContentProcess);
-
     if (mHasDefaultValue) {
       aDomPref->defaultValue() = Some(dom::PrefValue());
       mDefaultValue.ToDomPrefValue(Type(), &aDomPref->defaultValue().ref());
@@ -596,8 +555,7 @@ class Pref {
       aDomPref->defaultValue() = Nothing();
     }
 
-    if (mHasUserValue &&
-        !(aDomPref->isSanitized() && sOmitBlocklistedPrefValues)) {
+    if (mHasUserValue) {
       aDomPref->userValue() = Some(dom::PrefValue());
       mUserValue.ToDomPrefValue(Type(), &aDomPref->userValue().ref());
     } else {
@@ -606,7 +564,6 @@ class Pref {
 
     MOZ_ASSERT(aDomPref->defaultValue().isNothing() ||
                aDomPref->userValue().isNothing() ||
-               (mIsSanitized && sOmitBlocklistedPrefValues) ||
                (aDomPref->defaultValue().ref().type() ==
                 aDomPref->userValue().ref().type()));
   }
@@ -616,7 +573,6 @@ class Pref {
     MOZ_ASSERT(mName == aDomPref.name());
 
     mIsLocked = aDomPref.isLocked();
-    mIsSanitized = aDomPref.isSanitized();
 
     const Maybe<dom::PrefValue>& defaultValue = aDomPref.defaultValue();
     bool defaultValueChanged = false;
@@ -762,11 +718,9 @@ class Pref {
   //
   // The grammar for the serialized prefs has the following form.
   //
-  // <pref>         = <type> <locked> <sanitized> ':' <name> ':' <value>? ':'
-  //                  <value>? '\n'
+  // <pref>         = <type> <locked> ':' <name> ':' <value>? ':' <value>? '\n'
   // <type>         = 'B' | 'I' | 'S'
   // <locked>       = 'L' | '-'
-  // <sanitized>    = 'S' | '-'
   // <name>         = <string-value>
   // <value>        = <bool-value> | <int-value> | <string-value>
   // <bool-value>   = 'T' | 'F'
@@ -793,26 +747,21 @@ class Pref {
   //   print it and inspect it easily in a debugger.
   //
   // Examples of unlocked boolean prefs:
-  // - "B--:8/my.bool1:F:T\n"
-  // - "B--:8/my.bool2:F:\n"
-  // - "B--:8/my.bool3::T\n"
-  //
-  // Examples of sanitized, unlocked boolean prefs:
-  // - "B-S:8/my.bool1:F:T\n"
-  // - "B-S:8/my.bool2:F:\n"
-  // - "B-S:8/my.bool3::T\n"
+  // - "B-:8/my.bool1:F:T\n"
+  // - "B-:8/my.bool2:F:\n"
+  // - "B-:8/my.bool3::T\n"
   //
   // Examples of locked integer prefs:
-  // - "IL-:7/my.int1:0:1\n"
-  // - "IL-:7/my.int2:123:\n"
-  // - "IL-:7/my.int3::-99\n"
+  // - "IL:7/my.int1:0:1\n"
+  // - "IL:7/my.int2:123:\n"
+  // - "IL:7/my.int3::-99\n"
   //
   // Examples of unlocked string prefs:
-  // - "S--:10/my.string1:3/abc:4/wxyz\n"
-  // - "S--:10/my.string2:5/1.234:\n"
-  // - "S--:10/my.string3::7/string!\n"
+  // - "S-:10/my.string1:3/abc:4/wxyz\n"
+  // - "S-:10/my.string2:5/1.234:\n"
+  // - "S-:10/my.string3::7/string!\n"
 
-  void SerializeAndAppend(nsCString& aStr, bool aSanitizeUserValue) {
+  void SerializeAndAppend(nsCString& aStr) {
     switch (Type()) {
       case PrefType::Bool:
         aStr.Append('B');
@@ -833,7 +782,6 @@ class Pref {
     }
 
     aStr.Append(mIsLocked ? 'L' : '-');
-    aStr.Append(aSanitizeUserValue ? 'S' : '-');
     aStr.Append(':');
 
     SerializeAndAppendString(mName, aStr);
@@ -844,7 +792,7 @@ class Pref {
     }
     aStr.Append(':');
 
-    if (mHasUserValue && !(aSanitizeUserValue && sOmitBlocklistedPrefValues)) {
+    if (mHasUserValue) {
       mUserValue.SerializeAndAppend(Type(), aStr);
     }
     aStr.Append('\n');
@@ -879,18 +827,6 @@ class Pref {
     }
     p++;  // move past the isLocked char
 
-    // Sanitize?
-    bool isSanitized;
-    if (*p == 'S') {
-      isSanitized = true;
-    } else if (*p == '-') {
-      isSanitized = false;
-    } else {
-      NS_ERROR("bad pref sanitized status");
-      isSanitized = false;
-    }
-    p++;  // move past the isSanitized char
-
     MOZ_ASSERT(*p == ':');
     p++;  // move past the ':'
 
@@ -919,8 +855,7 @@ class Pref {
     MOZ_ASSERT(*p == '\n');
     p++;  // move past the '\n' following the user value
 
-    *aDomPref = dom::Pref(name, isLocked, isSanitized, maybeDefaultValue,
-                          maybeUserValue);
+    *aDomPref = dom::Pref(name, isLocked, maybeDefaultValue, maybeUserValue);
 
     return p;
   }
@@ -938,17 +873,12 @@ class Pref {
     }
   }
 
-  void RelocateName(NameArena* aArena) {
-    mName.Rebind(ArenaStrdup(mName.get(), *aArena), mName.Length());
-  }
-
  private:
-  nsDependentCString mName;  // allocated in sPrefNameArena
+  const nsDependentCString mName;  // allocated in sPrefNameArena
 
   uint32_t mType : 2;
   uint32_t mIsSticky : 1;
   uint32_t mIsLocked : 1;
-  uint32_t mIsSanitized : 1;
   uint32_t mHasDefaultValue : 1;
   uint32_t mHasUserValue : 1;
   uint32_t mIsSkippedByIteration : 1;
@@ -1000,7 +930,6 @@ class MOZ_STACK_CLASS PrefWrapper : public PrefWrapperBase {
   }
 
   FORWARD(bool, IsLocked)
-  FORWARD(bool, IsSanitized)
   FORWARD(bool, IsSticky)
   FORWARD(bool, HasDefaultValue)
   FORWARD(bool, HasUserValue)
@@ -1155,7 +1084,6 @@ void Pref::FromWrapper(PrefWrapper& aWrapper) {
   mType = uint32_t(pref.Type());
 
   mIsLocked = pref.IsLocked();
-  mIsSanitized = pref.IsSanitized();
   mIsSticky = pref.IsSticky();
 
   mHasDefaultValue = pref.HasDefaultValue();
@@ -2593,16 +2521,6 @@ nsPrefBranch::PrefIsLocked(const char* aPrefName, bool* aRetVal) {
   return NS_OK;
 }
 
-NS_IMETHODIMP
-nsPrefBranch::PrefIsSanitized(const char* aPrefName, bool* aRetVal) {
-  NS_ENSURE_ARG_POINTER(aRetVal);
-  NS_ENSURE_ARG(aPrefName);
-
-  const PrefName& pref = GetPrefName(aPrefName);
-  *aRetVal = Preferences::IsSanitized(pref.get());
-  return NS_OK;
-}
-
 NS_IMETHODIMP
 nsPrefBranch::UnlockPref(const char* aPrefName) {
   NS_ENSURE_ARG(aPrefName);
@@ -3628,18 +3546,18 @@ NS_IMPL_ISUPPORTS(Preferences, nsIPrefService, nsIObserver, nsIPrefBranch,
                   nsISupportsWeakReference)
 
 /* static */
-void Preferences::SerializePreferences(nsCString& aStr,
-                                       bool aIsDestinationWebContentProcess) {
+void Preferences::SerializePreferences(
+    nsCString& aStr,
+    const std::function<bool(const char*)>& aShouldSerializeFn) {
   MOZ_RELEASE_ASSERT(InitStaticMembers());
 
   aStr.Truncate();
 
   for (auto iter = HashTable()->iter(); !iter.done(); iter.next()) {
     Pref* pref = iter.get().get();
-    if (!pref->IsTypeNone() && pref->HasAdvisablySizedValues()) {
-      pref->SerializeAndAppend(
-          aStr,
-          ShouldSanitizePreference(pref, aIsDestinationWebContentProcess));
+    if (!pref->IsTypeNone() && pref->HasAdvisablySizedValues() &&
+        aShouldSerializeFn(pref->Name())) {
+      pref->SerializeAndAppend(aStr);
     }
   }
 
@@ -3684,21 +3602,12 @@ static void RegisterOncePrefs(SharedPrefMapBuilder& aBuilder);
 /* static */
 FileDescriptor Preferences::EnsureSnapshot(size_t* aSize) {
   MOZ_ASSERT(XRE_IsParentProcess());
-  MOZ_ASSERT(NS_IsMainThread());
 
   if (!gSharedMap) {
     SharedPrefMapBuilder builder;
 
-    nsTArray<Pref*> toRepopulate;
-    NameArena* newPrefNameArena = new NameArena();
-    for (auto iter = HashTable()->modIter(); !iter.done(); iter.next()) {
-      if (!ShouldSanitizePreference(iter.get().get(), true)) {
-        iter.get()->AddToMap(builder);
-      } else {
-        Pref* pref = iter.getMutable().release();
-        pref->RelocateName(newPrefNameArena);
-        toRepopulate.AppendElement(pref);
-      }
+    for (auto iter = HashTable()->iter(); !iter.done(); iter.next()) {
+      iter.get()->AddToMap(builder);
     }
 
     // Store the current value of `once`-mirrored prefs. After this point they
@@ -3719,16 +3628,8 @@ FileDescriptor Preferences::EnsureSnapshot(size_t* aSize) {
     HashTable()->clearAndCompact();
     Unused << HashTable()->reserve(kHashTableInitialLengthContent);
 
-    delete sPrefNameArena;
-    sPrefNameArena = newPrefNameArena;
+    PrefNameArena().Clear();
     gCallbackPref = nullptr;
-
-    for (uint32_t i = 0; i < toRepopulate.Length(); i++) {
-      auto pref = toRepopulate[i];
-      auto p = HashTable()->lookupForAdd(pref->Name());
-      MOZ_ASSERT(!p.found());
-      Unused << HashTable()->add(p, pref);
-    }
   }
 
   *aSize = gSharedMap->MapSize();
@@ -3973,18 +3874,12 @@ void Preferences::SetPreference(const dom::Pref& aDomPref) {
 }
 
 /* static */
-void Preferences::GetPreference(dom::Pref* aDomPref,
-                                const GeckoProcessType aDestinationProcessType,
-                                const nsACString& aDestinationRemoteType) {
+void Preferences::GetPreference(dom::Pref* aDomPref) {
   MOZ_ASSERT(XRE_IsParentProcess());
-  bool destIsWebContent =
-      aDestinationProcessType == GeckoProcessType_Content &&
-      (StringBeginsWith(aDestinationRemoteType, WEB_REMOTE_TYPE) ||
-       StringBeginsWith(aDestinationRemoteType, PREALLOC_REMOTE_TYPE));
 
   Pref* pref = pref_HashTableLookup(aDomPref->name().get());
   if (pref && pref->HasAdvisablySizedValues()) {
-    pref->ToDomPref(aDomPref, destIsWebContent);
+    pref->ToDomPref(aDomPref);
   }
 }
 
@@ -5080,14 +4975,6 @@ bool Preferences::IsLocked(const char* aPrefName) {
   return pref.isSome() && pref->IsLocked();
 }
 
-/* static */
-bool Preferences::IsSanitized(const char* aPrefName) {
-  NS_ENSURE_TRUE(InitStaticMembers(), false);
-
-  Maybe<PrefWrapper> pref = pref_Lookup(aPrefName);
-  return pref.isSome() && pref->IsSanitized();
-}
-
 /* static */
 nsresult Preferences::ClearUser(const char* aPrefName) {
   ENSURE_PARENT_PROCESS("ClearUser", aPrefName);
@@ -5741,114 +5628,6 @@ void UnloadPrefsModule() { Preferences::Shutdown(); }
 
 }  // namespace mozilla
 
-// Preference Sanitization Related Code ---------------------------------------
-
-#define PREF_LIST_ENTRY(s) \
-  { s, (sizeof(s) / sizeof(char)) - 1 }
-
-struct PrefListEntry {
-  const char* mPrefBranch;
-  size_t mLen;
-};
-
-// These prefs are not useful in child processes.
-static const PrefListEntry sParentOnlyPrefBranchList[] = {
-    PREF_LIST_ENTRY("app.update.lastUpdateTime."),
-    PREF_LIST_ENTRY("datareporting.policy."),
-    PREF_LIST_ENTRY("browser.safebrowsing.provider."),
-    PREF_LIST_ENTRY("browser.shell."), PREF_LIST_ENTRY("browser.slowStartup."),
-    // PREF_LIST_ENTRY("browser.startup."),
-    PREF_LIST_ENTRY("extensions.getAddons.cache."),
-    PREF_LIST_ENTRY("media.gmp-manager."),
-    PREF_LIST_ENTRY("media.gmp-gmpopenh264."),
-    // PREF_LIST_ENTRY("privacy.sanitize."),
-};
-
-static const PrefListEntry sDynamicPrefOverrideList[]{
-    PREF_LIST_ENTRY("print.printer_")};
-
-#undef PREF_LIST_ENTRY
-
-// Forward Declaration - it's not defined in the .h, because we don't need to;
-// it's only used here.
-template <class T>
-static bool ShouldSanitizePreference_Impl(const T& aPref,
-                                          bool aIsDestWebContentProcess);
-
-static bool ShouldSanitizePreference(const Pref* const aPref,
-                                     bool aIsDestWebContentProcess) {
-  return ShouldSanitizePreference_Impl(*aPref, aIsDestWebContentProcess);
-}
-
-static bool ShouldSanitizePreference(const PrefWrapper& aPref,
-                                     bool aIsDestWebContentProcess) {
-  return ShouldSanitizePreference_Impl(aPref, aIsDestWebContentProcess);
-}
-
-template <class T>
-static bool ShouldSanitizePreference_Impl(const T& aPref,
-                                          bool aIsDestWebContentProcess) {
-  // In the parent process, we use a heuristic to decide if a pref
-  // value should be sanitized before sending to subprocesses.
-  if (XRE_IsParentProcess()) {
-    const char* prefName = aPref.Name();
-
-    // First check against the denylist, the denylist is used for
-    // all subprocesses to reduce IPC traffic.
-    for (const auto& entry : sParentOnlyPrefBranchList) {
-      if (strncmp(entry.mPrefBranch, prefName, entry.mLen) == 0) {
-        return true;
-      }
-    }
-
-    if (!aIsDestWebContentProcess) {
-      return false;
-    }
-
-    // If it's a Web Content Process, also check if it's a dynamically
-    // named string preference
-    if (aPref.Type() == PrefType::String && !aPref.HasDefaultValue()) {
-      for (const auto& entry : sDynamicPrefOverrideList) {
-        if (strncmp(entry.mPrefBranch, prefName, entry.mLen) == 0) {
-          return false;
-        }
-      }
-      return true;
-    }
-
-    return false;
-  }
-
-  // In subprocesses we only check the sanitized bit
-  return aPref.IsSanitized();
-}
-
-namespace mozilla {
-
-// Of these four ShouldSanitizePreference* fuctions, this is the
-// only one exposed outside of Preferences.cpp, because this is the
-// only one ever called from outside this file.
-bool ShouldSanitizePreference(const char* aPrefName,
-                              bool aIsDestWebContentProcess) {
-  if (!aIsDestWebContentProcess) {
-    return false;
-  }
-
-  if (Maybe<PrefWrapper> pref = pref_Lookup(aPrefName)) {
-    if (pref.isNothing()) {
-      return true;
-    }
-    return ShouldSanitizePreference(pref.value(), aIsDestWebContentProcess);
-  }
-
-  return true;
-}
-
-Atomic<bool, Relaxed> sOmitBlocklistedPrefValues(false);
-Atomic<bool, Relaxed> sCrashOnBlocklistedPref(false);
-
-}  // namespace mozilla
-
 // This file contains the C wrappers for the C++ static pref getters, as used
 // by Rust code.
 #include "init/StaticPrefsCGetters.cpp"
diff --git a/modules/libpref/Preferences.h b/modules/libpref/Preferences.h
index 91050f5934e2..682a465a1ee9 100644
--- a/modules/libpref/Preferences.h
+++ b/modules/libpref/Preferences.h
@@ -23,7 +23,6 @@
 #include "nsString.h"
 #include "nsTArray.h"
 #include "nsWeakReference.h"
-#include "nsXULAppAPI.h"
 #include <atomic>
 #include <functional>
 
@@ -217,7 +216,6 @@ class Preferences final : public nsIPrefService,
   static nsresult Lock(const char* aPrefName);
   static nsresult Unlock(const char* aPrefName);
   static bool IsLocked(const char* aPrefName);
-  static bool IsSanitized(const char* aPrefName);
 
   // Clears user set pref. Fails if run outside the parent process.
   static nsresult ClearUser(const char* aPrefName);
@@ -400,8 +398,9 @@ class Preferences final : public nsIPrefService,
 
   // When a content process is created these methods are used to pass changed
   // prefs in bulk from the parent process, via shared memory.
-  static void SerializePreferences(nsCString& aStr,
-                                   bool aIsDestinationWebContentProcess);
+  static void SerializePreferences(
+      nsCString& aStr,
+      const std::function<bool(const char*)>& aShouldSerializeFn);
   static void DeserializePreferences(char* aStr, size_t aPrefsLen);
 
   static mozilla::ipc::FileDescriptor EnsureSnapshot(size_t* aSize);
@@ -409,9 +408,7 @@ class Preferences final : public nsIPrefService,
 
   // When a single pref is changed in the parent process, these methods are
   // used to pass the update to content processes.
-  static void GetPreference(dom::Pref* aPref,
-                            const GeckoProcessType aDestinationProcessType,
-                            const nsACString& aDestinationRemoteType);
+  static void GetPreference(dom::Pref* aPref);
   static void SetPreference(const dom::Pref& aPref);
 
 #ifdef DEBUG
@@ -534,11 +531,6 @@ class Preferences final : public nsIPrefService,
   static bool InitStaticMembers();
 };
 
-extern Atomic<bool, Relaxed> sOmitBlocklistedPrefValues;
-extern Atomic<bool, Relaxed> sCrashOnBlocklistedPref;
-
-bool ShouldSanitizePreference(const char* aPref, bool aIsDestWebContentProcess);
-
 }  // namespace mozilla
 
 #endif  // mozilla_Preferences_h
diff --git a/modules/libpref/SharedPrefMap.cpp b/modules/libpref/SharedPrefMap.cpp
index 81f8d9248537..a1f1774ab564 100644
--- a/modules/libpref/SharedPrefMap.cpp
+++ b/modules/libpref/SharedPrefMap.cpp
@@ -81,7 +81,6 @@ void SharedPrefMapBuilder::Add(const nsCString& aKey, const Flags& aFlags,
       aFlags.mHasUserValue,
       aFlags.mIsSticky,
       aFlags.mIsLocked,
-      aFlags.mIsSanitized,
       aFlags.mIsSkippedByIteration,
   });
 }
@@ -104,7 +103,6 @@ void SharedPrefMapBuilder::Add(const nsCString& aKey, const Flags& aFlags,
       aFlags.mHasUserValue,
       aFlags.mIsSticky,
       aFlags.mIsLocked,
-      aFlags.mIsSanitized,
       aFlags.mIsSkippedByIteration,
   });
 }
@@ -130,7 +128,6 @@ void SharedPrefMapBuilder::Add(const nsCString& aKey, const Flags& aFlags,
       aFlags.mHasUserValue,
       aFlags.mIsSticky,
       aFlags.mIsLocked,
-      aFlags.mIsSanitized,
       aFlags.mIsSkippedByIteration,
   });
 }
@@ -193,15 +190,10 @@ Result<Ok, nsresult> SharedPrefMapBuilder::Finalize(loader::AutoMemMap& aMap) {
   auto* entryPtr = reinterpret_cast<SharedPrefMap::Entry*>(&headerPtr[1]);
   for (auto* entry : entries) {
     *entryPtr = {
-        entry->mKey,
-        GetValue(*entry),
-        entry->mType,
-        entry->mHasDefaultValue,
-        entry->mHasUserValue,
-        entry->mIsSticky,
-        entry->mIsLocked,
-        entry->mIsSanitized,
-        entry->mIsSkippedByIteration,
+        entry->mKey,          GetValue(*entry),
+        entry->mType,         entry->mHasDefaultValue,
+        entry->mHasUserValue, entry->mIsSticky,
+        entry->mIsLocked,     entry->mIsSkippedByIteration,
     };
     entryPtr++;
   }
diff --git a/modules/libpref/SharedPrefMap.h b/modules/libpref/SharedPrefMap.h
index 7c949e137d80..2ae92ec04d76 100644
--- a/modules/libpref/SharedPrefMap.h
+++ b/modules/libpref/SharedPrefMap.h
@@ -307,9 +307,6 @@ class SharedPrefMap {
     uint8_t mIsSticky : 1;
     // True if the preference is locked, as defined by the preference service.
     uint8_t mIsLocked : 1;
-    // True if the preference is sanitized, as defined by the preference
-    // service.
-    uint8_t mIsSanitized : 1;
     // True if the preference should be skipped while iterating over the
     // SharedPrefMap. This is used to internally store Once StaticPrefs.
     // This property is not visible to users the way sticky and locked are.
@@ -342,7 +339,6 @@ class SharedPrefMap {
     bool HasDefaultValue() const { return mEntry->mHasDefaultValue; }
     bool HasUserValue() const { return mEntry->mHasUserValue; }
     bool IsLocked() const { return mEntry->mIsLocked; }
-    bool IsSanitized() const { return mEntry->mIsSanitized; }
     bool IsSticky() const { return mEntry->mIsSticky; }
     bool IsSkippedByIteration() const { return mEntry->mIsSkippedByIteration; }
 
@@ -573,7 +569,6 @@ class MOZ_RAII SharedPrefMapBuilder {
     uint8_t mHasUserValue : 1;
     uint8_t mIsSticky : 1;
     uint8_t mIsLocked : 1;
-    uint8_t mIsSanitized : 1;
     uint8_t mIsSkippedByIteration : 1;
   };
 
@@ -812,7 +807,6 @@ class MOZ_RAII SharedPrefMapBuilder {
     uint8_t mHasUserValue : 1;
     uint8_t mIsSticky : 1;
     uint8_t mIsLocked : 1;
-    uint8_t mIsSanitized : 1;
     uint8_t mIsSkippedByIteration : 1;
   };
 
diff --git a/modules/libpref/StaticPrefsBase.h b/modules/libpref/StaticPrefsBase.h
index f1cc5a5e4f34..23df6d918b52 100644
--- a/modules/libpref/StaticPrefsBase.h
+++ b/modules/libpref/StaticPrefsBase.h
@@ -19,12 +19,6 @@ class SharedPrefMapBuilder;
 
 typedef const char* String;
 
-template <typename T>
-struct IsString : std::false_type {};
-
-template <>
-struct IsString<String> : std::true_type {};
-
 typedef Atomic<bool, Relaxed> RelaxedAtomicBool;
 typedef Atomic<bool, ReleaseAcquire> ReleaseAcquireAtomicBool;
 typedef Atomic<bool, SequentiallyConsistent> SequentiallyConsistentAtomicBool;
diff --git a/modules/libpref/docs/index.md b/modules/libpref/docs/index.md
index 40c8977015bb..d0e16fec0c25 100644
--- a/modules/libpref/docs/index.md
+++ b/modules/libpref/docs/index.md
@@ -159,23 +159,6 @@ variable if the pref is deleted? Currently there is a missing
 the deletion. The cleanest solution is probably to disallow static prefs from
 being deleted.
 
-### Sanitized Prefs
-We restrict certain prefs from entering certain subprocesses. In subprocesses,
-a preference may be marked as 'Sanitized' to indicate that it may or may not
-have a user value, but that value is not present in this process.  In the
-parent process no pref is marked as Sanitized.
-
-Pref Sanitization is overloaded for two purposes:
- 1. To protect private user data that may be stored in preferences from a
-    Spectre adversary.
- 2. To reduce IPC use for commonly modified preferences.
-
-A pref is sanitized from entering the web content process if it matches a
-denylist _or_ it is a dynamically-named string preference.
-
-A pref is sanitized from entering other subprocesses if it matches the
-denylist.
-
 ### Loading and Saving
 Default pref values are initialized from various pref data files. Notable ones
 include:
@@ -231,10 +214,10 @@ activity.
 ### about:support
 about:support contains an "Important Modified Preferences" table. It contains
 all prefs that (a) have had their value changed from the default, and (b) whose
-prefix match a allowlist in `Troubleshoot.jsm`. The allowlist matching is to
+prefix match a whitelist in `Troubleshoot.jsm`. The whitelist matching is to
 avoid exposing pref values that might be privacy-sensitive.
 
-**Problem:** The allowlist of prefixes is specified separately from the prefs
+**Problem:** The whitelist of prefixes is specified separately from the prefs
 themselves. Having an attribute on a pref definition would be better.
 
 ### Sync
@@ -366,22 +349,18 @@ process. They exist so that all child processes can be given the same `once`
 values as the parent process.
 
 ### Child process startup (parent side)
-When the first child process is created, the parent process serializes most of
-its hash table into a shared, immutable snapshot. This snapshot is stored in a
-shared memory region managed by a `SharedPrefMap` instance. 
-
-Sanitized preferences (matching _either_ the denylist of the dynamically named
-heuristic) are not included in the shared memory region. After building the
-shared memory region, the parent process clears the hash table and then
-re-enters sanitized prefs into it. Besides the sanitized prefs, the hash table
-is subsequently used only to store changed pref values.
+When the first child process is created, the parent process serializes its hash
+table into a shared, immutable snapshot. This snapshot is stored in a shared
+memory region managed by a `SharedPrefMap` instance. The parent process then
+clears the hash table. The hash table is subsequently used only to store
+changed pref values.
 
 When any child process is created, the parent process serializes all pref
 values present in the hash table (i.e. those that have changed since the
-snapshot was made) _except sanitized prefs__ and stores them in a second,
-short-lived shared memory region. This represents the set of changes the child
-process needs to apply on top of the snapshot, and allows it to build a hash
-table which should exactly match the parent's, modulo the sanitized prefs.
+snapshot was made) and stores them in a second, short-lived shared memory
+region. This represents the set of changes the child process needs to apply on
+top of the snapshot, and allows it to build a hash table which should exactly
+match the parent's.
 
 The parent process passes two file descriptors to the child process, one for
 each region of memory. The snapshot is the same for all child processes.
@@ -442,13 +421,15 @@ want to waste memory creating an unnecessary hash table entry.
 
 Content processes must be told about any visible pref value changes. (A change
 to a default value that is hidden by a user value is unimportant.) When this
-happens, `ContentParent` detects the change (via an observer).  Sanitized prefs
-do not produce an update; and for string prefs it also checks the value(s)
-don't exceed 4 KiB. If the checks pass, it sends an IPC message
-(`PreferenceUpdate`) to the child process, and the child process updates the
-pref (default and user value) accordingly.
+happens, `ContentParent` detects the change (via an observer).  It checks the
+pref name against a small blacklist of prefixes that child processes should not
+care about (this is an optimization to reduce IPC rather than a
+capabilities/security consideration), and for string prefs it also checks the
+value(s) don't exceed 4 KiB. If the checks pass, it sends an IPC message
+(`PreferenceUpdate`) to the child process, and the child process updates
+the pref (default and user value) accordingly.
 
-**Problem:** The denylist of prefixes is specified separately from the prefs
+**Problem:** The blacklist of prefixes is specified separately from the prefs
 themselves. Having an attribute on a pref definition would be better.
 
 **Problem:** The 4 KiB limit can lead to inconsistencies between the parent
diff --git a/modules/libpref/init/StaticPrefList.yaml b/modules/libpref/init/StaticPrefList.yaml
index 0775142957a7..7b0ddf8196ea 100644
--- a/modules/libpref/init/StaticPrefList.yaml
+++ b/modules/libpref/init/StaticPrefList.yaml
@@ -4697,18 +4697,6 @@
   value: @IS_ANDROID@
   mirror: always
 
-# If true, do not sent blocklisted preference values to the subprocess
-- name: fission.omitBlocklistedPrefsInSubprocesses
-  type: RelaxedAtomicBool
-  value: false
-  mirror: always
-
-# If true, crash when a blocklisted preference is accessed in a subprocess
-- name: fission.enforceBlocklistedPrefsInSubprocesses
-  type: RelaxedAtomicBool
-  value: false
-  mirror: always
-
 #---------------------------------------------------------------------------
 # Prefs starting with "font."
 #---------------------------------------------------------------------------
diff --git a/modules/libpref/init/StaticPrefListBegin.h b/modules/libpref/init/StaticPrefListBegin.h
index 8af91795549b..71b2cb505d39 100644
--- a/modules/libpref/init/StaticPrefListBegin.h
+++ b/modules/libpref/init/StaticPrefListBegin.h
@@ -9,9 +9,7 @@
 // namespace.
 
 #include "StaticPrefsBase.h"
-#include "Preferences.h"
 #include "MainThreadUtils.h"  // for NS_IsMainThread()
-#include "nsXULAppAPI.h"      // for XRE_IsContentProcess()
 
 namespace mozilla {
 namespace StaticPrefs {
@@ -19,35 +17,23 @@ namespace StaticPrefs {
 // For mirrored prefs we generate an extern variable declaration and three
 // getter declarations/definitions.
 #define NEVER_PREF(name, cpp_type, default_value)
-#define ALWAYS_PREF(name, base_id, full_id, cpp_type, default_value)           \
-  extern cpp_type sMirror_##full_id;                                           \
-  inline StripAtomic<cpp_type> full_id() {                                     \
-    if (!XRE_IsParentProcess() && IsString<cpp_type>::value &&                 \
-        sCrashOnBlocklistedPref) {                                             \
-      MOZ_DIAGNOSTIC_ASSERT(                                                   \
-          !ShouldSanitizePreference(name, XRE_IsContentProcess()),             \
-          "Should not access the preference '" name "' in Content Processes"); \
-    }                                                                          \
-    MOZ_DIAGNOSTIC_ASSERT(IsAtomic<cpp_type>::value || NS_IsMainThread(),      \
-                          "Non-atomic static pref '" name                      \
-                          "' being accessed on background thread by getter");  \
-    return sMirror_##full_id;                                                  \
-  }                                                                            \
-  inline const char* GetPrefName_##base_id() { return name; }                  \
-  inline StripAtomic<cpp_type> GetPrefDefault_##base_id() {                    \
-    return default_value;                                                      \
+#define ALWAYS_PREF(name, base_id, full_id, cpp_type, default_value)          \
+  extern cpp_type sMirror_##full_id;                                          \
+  inline StripAtomic<cpp_type> full_id() {                                    \
+    MOZ_DIAGNOSTIC_ASSERT(IsAtomic<cpp_type>::value || NS_IsMainThread(),     \
+                          "Non-atomic static pref '" name                     \
+                          "' being accessed on background thread by getter"); \
+    return sMirror_##full_id;                                                 \
+  }                                                                           \
+  inline const char* GetPrefName_##base_id() { return name; }                 \
+  inline StripAtomic<cpp_type> GetPrefDefault_##base_id() {                   \
+    return default_value;                                                     \
   }
-#define ONCE_PREF(name, base_id, full_id, cpp_type, default_value)             \
-  extern cpp_type sMirror_##full_id;                                           \
-  inline cpp_type full_id() {                                                  \
-    MaybeInitOncePrefs();                                                      \
-    if (!XRE_IsParentProcess() && IsString<cpp_type>::value &&                 \
-        sCrashOnBlocklistedPref) {                                             \
-      MOZ_DIAGNOSTIC_ASSERT(                                                   \
-          !ShouldSanitizePreference(name, XRE_IsContentProcess()),             \
-          "Should not access the preference '" name "' in Content Processes"); \
-    }                                                                          \
-    return sMirror_##full_id;                                                  \
-  }                                                                            \
-  inline const char* GetPrefName_##base_id() { return name; }                  \
+#define ONCE_PREF(name, base_id, full_id, cpp_type, default_value) \
+  extern cpp_type sMirror_##full_id;                               \
+  inline cpp_type full_id() {                                      \
+    MaybeInitOncePrefs();                                          \
+    return sMirror_##full_id;                                      \
+  }                                                                \
+  inline const char* GetPrefName_##base_id() { return name; }      \
   inline cpp_type GetPrefDefault_##base_id() { return default_value; }
diff --git a/modules/libpref/nsIPrefBranch.idl b/modules/libpref/nsIPrefBranch.idl
index 8e45d5d3122f..1a567ba3b26f 100644
--- a/modules/libpref/nsIPrefBranch.idl
+++ b/modules/libpref/nsIPrefBranch.idl
@@ -315,24 +315,6 @@ interface nsIPrefBranch : nsISupports
    */
   boolean prefIsLocked(in string aPrefName);
 
-  /**
-   * Called to check if a specific preference has been sanitized. If a
-   * preference is sanitized, any user value the preference may have will not
-   * be present in a sub-process.  A preference is never sanitized in the
-   * parent process; it is only marked as sanitized when it is converted
-   * to a dom::Pref for serialization to a child process.
-   *
-   * @param aPrefName The preference to be tested.
-   *
-   * @note
-   * This method can be called on either a default or user branch but it
-   * makes no difference.
-   *
-   * @return boolean  true  The preference is sanitized.
-   *                  false The preference is not sanitized.
-   */
-  boolean prefIsSanitized(in string aPrefName);
-
   /**
    * Called to unlock a specific preference. Unlocking a previously locked
    * preference allows the preference service to once again return the user set
diff --git a/modules/libpref/test/gtest/Basics.cpp b/modules/libpref/test/gtest/Basics.cpp
index 66299f61644f..8f6e0bef1fc3 100644
--- a/modules/libpref/test/gtest/Basics.cpp
+++ b/modules/libpref/test/gtest/Basics.cpp
@@ -43,13 +43,12 @@ TEST(PrefsBasics, Serialize)
             true);
 
   nsCString str;
-  Preferences::SerializePreferences(str, true);
-  fprintf(stderr, "%s\n", str.Data());
-  // Assert that some prefs were not sanitized
-  ASSERT_NE(nullptr, strstr(str.Data(), "B--:"));
-  ASSERT_NE(nullptr, strstr(str.Data(), "I--:"));
-  ASSERT_NE(nullptr, strstr(str.Data(), "S--:"));
-  // Assert that something was sanitized
-  ASSERT_NE(nullptr,
-            strstr(str.Data(), "S-S:36/media.gmp-manager.certs.1.commonName"));
+  Preferences::SerializePreferences(
+      str, [](const char* aPref) -> bool { return false; });
+  ASSERT_STREQ(str.Data(), "");
+
+  Preferences::SerializePreferences(str, [](const char* aPref) -> bool {
+    return strncmp(aPref, "foo.bool", 8) == 0;
+  });
+  ASSERT_STREQ(str.Data(), "B-:8/foo.bool:T:F\n");
 }
diff --git a/netwerk/base/nsIOService.cpp b/netwerk/base/nsIOService.cpp
index 035e3264c4f0..60b01e4eb55a 100644
--- a/netwerk/base/nsIOService.cpp
+++ b/netwerk/base/nsIOService.cpp
@@ -646,11 +646,8 @@ void nsIOService::NotifySocketProcessPrefsChanged(const char* aName) {
     return;
   }
 
-  dom::Pref pref(nsCString(aName), /* isLocked */ false,
-                 /* isSanitized */ false, Nothing(), Nothing());
-
-  Preferences::GetPreference(&pref, GeckoProcessType_Socket,
-                             /* remoteType */ ""_ns);
+  dom::Pref pref(nsCString(aName), /* isLocked */ false, Nothing(), Nothing());
+  Preferences::GetPreference(&pref);
   auto sendPrefUpdate = [pref]() {
     Unused << gIOService->mSocketProcess->GetActor()->SendPreferenceUpdate(
         pref);
diff --git a/netwerk/ipc/SocketProcessHost.cpp b/netwerk/ipc/SocketProcessHost.cpp
index 2677cd510353..b9e3ca93b512 100644
--- a/netwerk/ipc/SocketProcessHost.cpp
+++ b/netwerk/ipc/SocketProcessHost.cpp
@@ -68,9 +68,9 @@ bool SocketProcessHost::Launch() {
   std::vector<std::string> extraArgs;
   ProcessChild::AddPlatformBuildID(extraArgs);
 
-  SharedPreferenceSerializer prefSerializer;
-  if (!prefSerializer.SerializeToSharedMemory(GeckoProcessType_VR,
-                                              /* remoteType */ ""_ns)) {
+  SharedPreferenceSerializer prefSerializer(
+      mozilla::dom::ContentParent::ShouldSyncPreference);
+  if (!prefSerializer.SerializeToSharedMemory()) {
     return false;
   }
   prefSerializer.AddSharedPrefCmdLineArgs(*this, extraArgs);