diff --git a/browser/app/moz.build b/browser/app/moz.build
index c731e9798a..80617a4acc 100644
--- a/browser/app/moz.build
+++ b/browser/app/moz.build
@@ -172,3 +172,6 @@ for icon in ("firefox", "document", "newwindow", "newtab", "pbmode", "document_p
         CONFIG["MOZ_BRANDING_DIRECTORY"],
         icon,
     )
+
+# DOM Mask
+LOCAL_INCLUDES += ["/dom/mask"]
\ No newline at end of file
diff --git a/dom/base/Element.cpp b/dom/base/Element.cpp
index be31000278..6617ad3bd5 100644
--- a/dom/base/Element.cpp
+++ b/dom/base/Element.cpp
@@ -12,6 +12,7 @@
 
 #include "mozilla/dom/Element.h"
 #include "mozilla/dom/ElementInlines.h"
+#include "MaskConfig.hpp"
 
 #include <inttypes.h>
 #include <initializer_list>
@@ -984,6 +985,18 @@ nsRect Element::GetClientAreaRect() {
   Document* doc = OwnerDoc();
   nsPresContext* presContext = doc->GetPresContext();
 
+  if (doc->GetBodyElement() == this) {
+    if (auto conf = MaskConfig::GetInt32Rect(
+            "document.body.clientTop", "document.body.clientLeft",
+            "document.body.clientWidth", "document.body.clientHeight")) {
+      if (conf.has_value()) {
+        auto values = conf.value();
+        return nsRect(values[0] * 60, values[1] * 60, values[2] * 60,
+                      values[3] * 60);
+      }
+    }
+  }
+
   // We can avoid a layout flush if this is the scrolling element of the
   // document, we have overlay scrollbars, and we aren't embedded in another
   // document
diff --git a/dom/base/Navigator.cpp b/dom/base/Navigator.cpp
index 14a00b8ed8..7b6a0e4a10 100644
--- a/dom/base/Navigator.cpp
+++ b/dom/base/Navigator.cpp
@@ -8,6 +8,7 @@
 #include "base/basictypes.h"
 
 #include "Navigator.h"
+#include "MaskConfig.hpp"
 #include "nsIXULAppInfo.h"
 #include "nsPluginArray.h"
 #include "nsMimeTypeArray.h"
@@ -261,6 +262,8 @@ void Navigator::Invalidate() {
 
 void Navigator::GetUserAgent(nsAString& aUserAgent, CallerType aCallerType,
                              ErrorResult& aRv) const {
+  if (auto value = MaskConfig::GetString("navigator.userAgent"))
+    return aUserAgent.Assign(NS_ConvertUTF8toUTF16(value.value()));
   nsCOMPtr<nsPIDOMWindowInner> window;
 
   if (mWindow) {
@@ -287,6 +290,8 @@ void Navigator::GetUserAgent(nsAString& aUserAgent, CallerType aCallerType,
 }
 
 void Navigator::GetAppCodeName(nsAString& aAppCodeName, ErrorResult& aRv) {
+  if (auto value = MaskConfig::GetString("navigator.appCodeName"))
+    return aAppCodeName.Assign(NS_ConvertUTF8toUTF16(value.value()));
   nsresult rv;
 
   nsCOMPtr<nsIHttpProtocolHandler> service(
@@ -308,6 +313,8 @@ void Navigator::GetAppCodeName(nsAString& aAppCodeName, ErrorResult& aRv) {
 
 void Navigator::GetAppVersion(nsAString& aAppVersion, CallerType aCallerType,
                               ErrorResult& aRv) const {
+  if (auto value = MaskConfig::GetString("navigator.appVersion"))
+    return aAppVersion.Assign(NS_ConvertUTF8toUTF16(value.value()));
   nsCOMPtr<Document> doc = mWindow->GetExtantDoc();
 
   nsresult rv = GetAppVersion(
@@ -319,6 +326,8 @@ void Navigator::GetAppVersion(nsAString& aAppVersion, CallerType aCallerType,
 }
 
 void Navigator::GetAppName(nsAString& aAppName) const {
+  if (auto value = MaskConfig::GetString("navigator.appName"))
+    return aAppName.Assign(NS_ConvertUTF8toUTF16(value.value()));
   aAppName.AssignLiteral("Netscape");
 }
 
@@ -343,6 +352,15 @@ void Navigator::GetAcceptLanguages(nsTArray<nsString>& aLanguages) {
 
   aLanguages.Clear();
 
+  if (std::vector<std::string> maskValues =
+          MaskConfig::GetStringList("navigator.languages");
+      !maskValues.empty()) {
+    for (const auto& lang : maskValues) {
+      aLanguages.AppendElement(NS_ConvertUTF8toUTF16(lang));
+    }
+    return;
+  }
+
   // E.g. "de-de, en-us,en".
   nsAutoString acceptLang;
   Preferences::GetLocalizedString("intl.accept_languages", acceptLang);
@@ -390,6 +408,8 @@ void Navigator::GetAcceptLanguages(nsTArray<nsString>& aLanguages) {
  * Full details above in GetAcceptLanguages.
  */
 void Navigator::GetLanguage(nsAString& aLanguage) {
+  if (auto value = MaskConfig::GetString("navigator.language"))
+    return aLanguage.Assign(NS_ConvertUTF8toUTF16(value.value()));
   nsTArray<nsString> languages;
   GetLanguages(languages);
   MOZ_ASSERT(languages.Length() >= 1);
@@ -407,6 +427,8 @@ void Navigator::GetLanguages(nsTArray<nsString>& aLanguages) {
 
 void Navigator::GetPlatform(nsAString& aPlatform, CallerType aCallerType,
                             ErrorResult& aRv) const {
+  if (auto value = MaskConfig::GetString("navigator.platform"))
+    return aPlatform.Assign(NS_ConvertUTF8toUTF16(value.value()));
   if (mWindow) {
     BrowsingContext* bc = mWindow->GetBrowsingContext();
     nsString customPlatform;
@@ -433,6 +455,8 @@ void Navigator::GetPlatform(nsAString& aPlatform, CallerType aCallerType,
 void Navigator::GetOscpu(nsAString& aOSCPU, CallerType aCallerType,
                          ErrorResult& aRv) const {
   if (aCallerType != CallerType::System) {
+    if (auto value = MaskConfig::GetString("navigator.oscpu"))
+      return aOSCPU.Assign(NS_ConvertUTF8toUTF16(value.value()));
     // If fingerprinting resistance is on, we will spoof this value. See
     // nsRFPService.h for details about spoofed values.
     if (nsContentUtils::ShouldResistFingerprinting(GetDocShell(),
@@ -472,10 +496,14 @@ void Navigator::GetVendor(nsAString& aVendor) { aVendor.Truncate(); }
 void Navigator::GetVendorSub(nsAString& aVendorSub) { aVendorSub.Truncate(); }
 
 void Navigator::GetProduct(nsAString& aProduct) {
+  if (auto value = MaskConfig::GetString("navigator.product"))
+    return aProduct.Assign(NS_ConvertUTF8toUTF16(value.value()));
   aProduct.AssignLiteral("Gecko");
 }
 
 void Navigator::GetProductSub(nsAString& aProductSub) {
+  if (auto value = MaskConfig::GetString("navigator.productSub"))
+    return aProductSub.Assign(NS_ConvertUTF8toUTF16(value.value()));
   // Legacy build date hardcoded for backward compatibility (bug 776376)
   aProductSub.AssignLiteral(LEGACY_UA_GECKO_TRAIL);
 }
@@ -501,7 +529,11 @@ nsPluginArray* Navigator::GetPlugins(ErrorResult& aRv) {
   return mPlugins;
 }
 
-bool Navigator::PdfViewerEnabled() { return !StaticPrefs::pdfjs_disabled(); }
+bool Navigator::PdfViewerEnabled() {
+  if (auto value = MaskConfig::GetBool("pdfViewerEnabled"); value.has_value())
+    return value.value();
+  return !StaticPrefs::pdfjs_disabled();
+}
 
 Permissions* Navigator::GetPermissions(ErrorResult& aRv) {
   if (!mWindow) {
@@ -527,6 +559,9 @@ StorageManager* Navigator::Storage() {
 }
 
 bool Navigator::CookieEnabled() {
+  if (auto value = MaskConfig::GetBool("navigator.cookieEnabled");
+      value.has_value())
+    return value.value();
   // Check whether an exception overrides the global cookie behavior
   // Note that the code for getting the URI here matches that in
   // nsHTMLDocument::SetCookie.
@@ -573,6 +608,8 @@ bool Navigator::CookieEnabled() {
 }
 
 bool Navigator::OnLine() {
+  if (auto value = MaskConfig::GetBool("navigator.onLine"); value.has_value())
+    return value.value();
   if (mWindow) {
     // Check if this tab is set to be offline.
     BrowsingContext* bc = mWindow->GetBrowsingContext();
@@ -587,6 +624,8 @@ bool Navigator::OnLine() {
 void Navigator::GetBuildID(nsAString& aBuildID, CallerType aCallerType,
                            ErrorResult& aRv) const {
   if (aCallerType != CallerType::System) {
+    if (auto value = MaskConfig::GetString("navigator.buildID"))
+      return aBuildID.Assign(NS_ConvertUTF8toUTF16(value.value()));
     // If fingerprinting resistance is on, we will spoof this value. See
     // nsRFPService.h for details about spoofed values.
     if (nsContentUtils::ShouldResistFingerprinting(
@@ -643,6 +682,8 @@ void Navigator::GetBuildID(nsAString& aBuildID, CallerType aCallerType,
 }
 
 void Navigator::GetDoNotTrack(nsAString& aResult) {
+  if (auto value = MaskConfig::GetString("navigator.doNotTrack"))
+    return aResult.Assign(NS_ConvertUTF8toUTF16(value.value()));
   bool doNotTrack = StaticPrefs::privacy_donottrackheader_enabled();
   if (!doNotTrack) {
     nsCOMPtr<nsILoadContext> loadContext = do_GetInterface(mWindow);
@@ -657,6 +698,9 @@ void Navigator::GetDoNotTrack(nsAString& aResult) {
 }
 
 bool Navigator::GlobalPrivacyControl() {
+  if (auto value = MaskConfig::GetBool("navigator.globalPrivacyControl");
+      value.has_value())
+    return value.value();
   bool gpcStatus = StaticPrefs::privacy_globalprivacycontrol_enabled();
   if (!gpcStatus) {
     nsCOMPtr<nsILoadContext> loadContext = do_GetInterface(mWindow);
@@ -668,6 +712,8 @@ bool Navigator::GlobalPrivacyControl() {
 }
 
 uint64_t Navigator::HardwareConcurrency() {
+  if (auto value = MaskConfig::GetUint64("navigator.hardwareConcurrency"))
+    return value.value();
   workerinternals::RuntimeService* rts =
       workerinternals::RuntimeService::GetOrCreateService();
   if (!rts) {
@@ -872,6 +918,8 @@ bool Navigator::Vibrate(const nsTArray<uint32_t>& aPattern) {
 //*****************************************************************************
 
 uint32_t Navigator::MaxTouchPoints(CallerType aCallerType) {
+  if (auto value = MaskConfig::GetUint32("navigator.maxTouchPoints"))
+    return value.value();
   nsIDocShell* docshell = GetDocShell();
   BrowsingContext* bc = docshell ? docshell->GetBrowsingContext() : nullptr;
 
@@ -2261,6 +2309,7 @@ dom::LockManager* Navigator::Locks() {
 
 /* static */
 bool Navigator::Webdriver() {
+  return false;  // Never enable this
 #ifdef ENABLE_WEBDRIVER
   nsCOMPtr<nsIMarionette> marionette = do_GetService(NS_MARIONETTE_CONTRACTID);
   if (marionette) {
diff --git a/dom/base/moz.build b/dom/base/moz.build
index ef1780f161..4e4d038157 100644
--- a/dom/base/moz.build
+++ b/dom/base/moz.build
@@ -628,3 +628,6 @@ GeneratedFile(
         "/servo/components/style/properties/counted_unknown_properties.py",
     ],
 )
+
+# DOM Mask
+LOCAL_INCLUDES += ["/dom/mask"]
\ No newline at end of file
diff --git a/dom/base/nsGlobalWindowInner.cpp b/dom/base/nsGlobalWindowInner.cpp
index 5337e1588f..bff2f90321 100644
--- a/dom/base/nsGlobalWindowInner.cpp
+++ b/dom/base/nsGlobalWindowInner.cpp
@@ -5,6 +5,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "nsGlobalWindowInner.h"
+#include "MaskConfig.hpp"
 
 #include <inttypes.h>
 #include <stdio.h>
@@ -3408,6 +3409,8 @@ void nsGlobalWindowInner::SetName(const nsAString& aName,
 }
 
 double nsGlobalWindowInner::GetInnerWidth(ErrorResult& aError) {
+  if (auto value = MaskConfig::GetDouble("window.innerWidth"))
+    return value.value();
   FORWARD_TO_OUTER_OR_THROW(GetInnerWidthOuter, (aError), aError, 0);
 }
 
@@ -3419,6 +3422,8 @@ nsresult nsGlobalWindowInner::GetInnerWidth(double* aWidth) {
 }
 
 double nsGlobalWindowInner::GetInnerHeight(ErrorResult& aError) {
+  if (auto value = MaskConfig::GetDouble("window.innerHeight"))
+    return value.value();
   // We ignore aCallerType; we only have that argument because some other things
   // called by GetReplaceableWindowCoord need it.  If this ever changes, fix
   //   nsresult nsGlobalWindowInner::GetInnerHeight(double* aInnerWidth)
@@ -3435,12 +3440,16 @@ nsresult nsGlobalWindowInner::GetInnerHeight(double* aHeight) {
 
 int32_t nsGlobalWindowInner::GetOuterWidth(CallerType aCallerType,
                                            ErrorResult& aError) {
+  if (auto value = MaskConfig::GetInt32("window.outerWidth"))
+    return value.value();
   FORWARD_TO_OUTER_OR_THROW(GetOuterWidthOuter, (aCallerType, aError), aError,
                             0);
 }
 
 int32_t nsGlobalWindowInner::GetOuterHeight(CallerType aCallerType,
                                             ErrorResult& aError) {
+  if (auto value = MaskConfig::GetInt32("window.outerHeight"))
+    return value.value();
   FORWARD_TO_OUTER_OR_THROW(GetOuterHeightOuter, (aCallerType, aError), aError,
                             0);
 }
@@ -3455,11 +3464,13 @@ double nsGlobalWindowInner::ScreenEdgeSlopY() const {
 
 int32_t nsGlobalWindowInner::GetScreenX(CallerType aCallerType,
                                         ErrorResult& aError) {
+  if (auto value = MaskConfig::GetInt32("window.screenX")) return value.value();
   FORWARD_TO_OUTER_OR_THROW(GetScreenXOuter, (aCallerType, aError), aError, 0);
 }
 
 int32_t nsGlobalWindowInner::GetScreenY(CallerType aCallerType,
                                         ErrorResult& aError) {
+  if (auto value = MaskConfig::GetInt32("window.screenY")) return value.value();
   FORWARD_TO_OUTER_OR_THROW(GetScreenYOuter, (aCallerType, aError), aError, 0);
 }
 
@@ -3493,6 +3504,8 @@ static nsPresContext* GetPresContextForRatio(Document* aDoc) {
 double nsGlobalWindowInner::GetDevicePixelRatio(CallerType aCallerType,
                                                 ErrorResult& aError) {
   ENSURE_ACTIVE_DOCUMENT(aError, 0.0);
+  if (auto value = MaskConfig::GetDouble("window.devicePixelRatio"))
+    return value.value();
 
   RefPtr<nsPresContext> presContext = GetPresContextForRatio(mDoc);
   if (NS_WARN_IF(!presContext)) {
@@ -3574,26 +3587,38 @@ already_AddRefed<MediaQueryList> nsGlobalWindowInner::MatchMedia(
 }
 
 int32_t nsGlobalWindowInner::GetScrollMinX(ErrorResult& aError) {
+  if (auto value = MaskConfig::GetInt32("window.scrollMinX"))
+    return value.value();
   FORWARD_TO_OUTER_OR_THROW(GetScrollBoundaryOuter, (eSideLeft), aError, 0);
 }
 
 int32_t nsGlobalWindowInner::GetScrollMinY(ErrorResult& aError) {
+  if (auto value = MaskConfig::GetInt32("window.scrollMinY"))
+    return value.value();
   FORWARD_TO_OUTER_OR_THROW(GetScrollBoundaryOuter, (eSideTop), aError, 0);
 }
 
 int32_t nsGlobalWindowInner::GetScrollMaxX(ErrorResult& aError) {
+  if (auto value = MaskConfig::GetInt32("window.scrollMaxX"))
+    return value.value();
   FORWARD_TO_OUTER_OR_THROW(GetScrollBoundaryOuter, (eSideRight), aError, 0);
 }
 
 int32_t nsGlobalWindowInner::GetScrollMaxY(ErrorResult& aError) {
+  if (auto value = MaskConfig::GetInt32("window.scrollMaxY"))
+    return value.value();
   FORWARD_TO_OUTER_OR_THROW(GetScrollBoundaryOuter, (eSideBottom), aError, 0);
 }
 
 double nsGlobalWindowInner::GetScrollX(ErrorResult& aError) {
+  if (auto value = MaskConfig::GetDouble("screen.pageXOffset"))
+    return value.value();
   FORWARD_TO_OUTER_OR_THROW(GetScrollXOuter, (), aError, 0);
 }
 
 double nsGlobalWindowInner::GetScrollY(ErrorResult& aError) {
+  if (auto value = MaskConfig::GetDouble("screen.pageYOffset"))
+    return value.value();
   FORWARD_TO_OUTER_OR_THROW(GetScrollYOuter, (), aError, 0);
 }
 
diff --git a/dom/base/nsHistory.cpp b/dom/base/nsHistory.cpp
index 99994a73cc..837214d872 100644
--- a/dom/base/nsHistory.cpp
+++ b/dom/base/nsHistory.cpp
@@ -5,6 +5,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "nsHistory.h"
+#include "MaskConfig.hpp"
 
 #include "jsapi.h"
 #include "nsCOMPtr.h"
@@ -55,6 +56,8 @@ JSObject* nsHistory::WrapObject(JSContext* aCx,
 }
 
 uint32_t nsHistory::GetLength(ErrorResult& aRv) const {
+  if (auto value = MaskConfig::GetUint32("window.history.length"))
+    return value.value();
   nsCOMPtr<nsPIDOMWindowInner> win(do_QueryReferent(mInnerWindow));
   if (!win || !win->HasActiveDocument()) {
     aRv.Throw(NS_ERROR_DOM_SECURITY_ERR);
diff --git a/dom/base/nsScreen.cpp b/dom/base/nsScreen.cpp
index fc832fd2cf..f71a40edf1 100644
--- a/dom/base/nsScreen.cpp
+++ b/dom/base/nsScreen.cpp
@@ -4,6 +4,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+#include "MaskConfig.hpp"
 #include "nsContentUtils.h"
 #include "nsScreen.h"
 #include "mozilla/dom/Document.h"
@@ -37,6 +38,10 @@ NS_IMPL_CYCLE_COLLECTION_INHERITED(nsScreen, DOMEventTargetHelper,
                                    mScreenOrientation)
 
 int32_t nsScreen::PixelDepth() {
+  if (auto value = MaskConfig::GetUint32("screen.colorDepth"))
+    return value.value();
+  if (auto value = MaskConfig::GetUint32("screen.pixelDepth"))
+    return value.value();
   // Return 24 to prevent fingerprinting.
   if (ShouldResistFingerprinting(RFPTarget::ScreenPixelDepth)) {
     return 24;
@@ -60,6 +65,12 @@ nsDeviceContext* nsScreen::GetDeviceContext() const {
 }
 
 CSSIntRect nsScreen::GetRect() {
+  // Check for height and width overrides
+  if (auto height = MaskConfig::GetInt32("screen.height"),
+      width = MaskConfig::GetInt32("screen.width");
+      height && width) {
+    return {0, 0, width.value(), height.value()};
+  }
   // Return window inner rect to prevent fingerprinting.
   if (ShouldResistFingerprinting(RFPTarget::ScreenRect)) {
     return GetWindowInnerRect();
@@ -89,6 +100,12 @@ CSSIntRect nsScreen::GetRect() {
 }
 
 CSSIntRect nsScreen::GetAvailRect() {
+  auto rect = MaskConfig::GetRect("screen.availTop", "screen.availLeft",
+                                  "screen.availHeight", "screen.availWidth");
+  if (rect.has_value()) {
+    auto values = rect.value();
+    return {values[0], values[1], values[2], values[3]};
+  }
   // Return window inner rect to prevent fingerprinting.
   if (ShouldResistFingerprinting(RFPTarget::ScreenAvailRect)) {
     return GetWindowInnerRect();
diff --git a/dom/battery/BatteryManager.cpp b/dom/battery/BatteryManager.cpp
index 0a56f12af1..7a5b9a1a6c 100644
--- a/dom/battery/BatteryManager.cpp
+++ b/dom/battery/BatteryManager.cpp
@@ -7,6 +7,7 @@
 #include <cmath>
 #include <limits>
 #include "BatteryManager.h"
+#include "MaskConfig.hpp"
 #include "Constants.h"
 #include "mozilla/DOMEventTargetHelper.h"
 #include "mozilla/Hal.h"
@@ -50,6 +51,9 @@ JSObject* BatteryManager::WrapObject(JSContext* aCx,
 
 bool BatteryManager::Charging() const {
   MOZ_ASSERT(NS_IsMainThread());
+  if (auto value = MaskConfig::GetBool("battery:charging"); value.has_value())
+    return value.value();
+
   // For testing, unable to report the battery status information
   if (Preferences::GetBool("dom.battery.test.default", false)) {
     return true;
@@ -66,6 +70,8 @@ bool BatteryManager::Charging() const {
 
 double BatteryManager::DischargingTime() const {
   MOZ_ASSERT(NS_IsMainThread());
+  if (auto value = MaskConfig::GetDouble("battery:dischargingTime"))
+    return value.value();
   // For testing, unable to report the battery status information
   if (Preferences::GetBool("dom.battery.test.default", false)) {
     return std::numeric_limits<double>::infinity();
@@ -83,6 +89,8 @@ double BatteryManager::DischargingTime() const {
 
 double BatteryManager::ChargingTime() const {
   MOZ_ASSERT(NS_IsMainThread());
+  if (auto value = MaskConfig::GetDouble("battery:chargingTime"))
+    return value.value();
   // For testing, unable to report the battery status information
   if (Preferences::GetBool("dom.battery.test.default", false)) {
     return 0.0;
@@ -100,6 +108,7 @@ double BatteryManager::ChargingTime() const {
 
 double BatteryManager::Level() const {
   MOZ_ASSERT(NS_IsMainThread());
+  if (auto value = MaskConfig::GetDouble("battery:level")) return value.value();
   // For testing, unable to report the battery status information
   if (Preferences::GetBool("dom.battery.test.default")) {
     return 1.0;
diff --git a/dom/battery/moz.build b/dom/battery/moz.build
index 3a90c93c01..35e3227f5e 100644
--- a/dom/battery/moz.build
+++ b/dom/battery/moz.build
@@ -21,3 +21,6 @@ FINAL_LIBRARY = "xul"
 
 MOCHITEST_CHROME_MANIFESTS += ["test/chrome.toml"]
 MOCHITEST_MANIFESTS += ["test/mochitest.toml"]
+
+# DOM Mask
+LOCAL_INCLUDES += ["/dom/mask"]
\ No newline at end of file
diff --git a/dom/canvas/ClientWebGLContext.cpp b/dom/canvas/ClientWebGLContext.cpp
index 1614d2ead2..22b0f2584c 100644
--- a/dom/canvas/ClientWebGLContext.cpp
+++ b/dom/canvas/ClientWebGLContext.cpp
@@ -4,6 +4,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "ClientWebGLContext.h"
+#include "MaskConfig.hpp"
 
 #include <bitset>
 
@@ -2264,7 +2265,7 @@ void ClientWebGLContext::GetParameter(JSContext* cx, GLenum pname,
         retval.set(JS::NumberValue(state.mPixelUnpackState.skipRows));
         return;
     }  // switch pname
-  }    // if webgl2
+  }  // if webgl2
 
   // -
 
@@ -2336,6 +2337,10 @@ void ClientWebGLContext::GetParameter(JSContext* cx, GLenum pname,
 
         switch (pname) {
           case dom::WEBGL_debug_renderer_info_Binding::UNMASKED_RENDERER_WEBGL:
+            if (auto value = MaskConfig::GetString("webGl:renderer")) {
+              ret = Some(value.value());
+              break;
+            }
             ret = GetUnmaskedRenderer();
             if (ret && StaticPrefs::webgl_sanitize_unmasked_renderer()) {
               *ret = webgl::SanitizeRenderer(*ret);
@@ -2343,6 +2348,10 @@ void ClientWebGLContext::GetParameter(JSContext* cx, GLenum pname,
             break;
 
           case dom::WEBGL_debug_renderer_info_Binding::UNMASKED_VENDOR_WEBGL:
+            if (auto value = MaskConfig::GetString("webGl:vendor")) {
+              ret = Some(value.value());
+              break;
+            }
             ret = GetUnmaskedVendor();
             break;
 
diff --git a/dom/canvas/moz.build b/dom/canvas/moz.build
index 3a533d36d1..8697f8c21f 100644
--- a/dom/canvas/moz.build
+++ b/dom/canvas/moz.build
@@ -221,3 +221,6 @@ if CONFIG["CC_TYPE"] == "gcc":
 
 # Add libFuzzer configuration directives
 include("/tools/fuzzing/libfuzzer-config.mozbuild")
+
+# DOM Mask
+LOCAL_INCLUDES += ["/dom/mask"]
\ No newline at end of file
diff --git a/dom/moz.build b/dom/moz.build
index f781bd3708..9a66049d9b 100644
--- a/dom/moz.build
+++ b/dom/moz.build
@@ -115,3 +115,6 @@ if CONFIG["MOZ_WIDGET_TOOLKIT"] in ("gtk", "cocoa", "windows"):
     TEST_DIRS += ["plugins/test"]
 
 SPHINX_TREES["/dom"] = "docs"
+
+# DOM Mask
+DIRS += ["mask"]
\ No newline at end of file
diff --git a/dom/workers/WorkerNavigator.cpp b/dom/workers/WorkerNavigator.cpp
index 1be36bc7d4..2cdaff494f 100644
--- a/dom/workers/WorkerNavigator.cpp
+++ b/dom/workers/WorkerNavigator.cpp
@@ -5,6 +5,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "mozilla/dom/WorkerNavigator.h"
+#include "MaskConfig.hpp"
 
 #include <utility>
 
@@ -92,6 +93,9 @@ JSObject* WorkerNavigator::WrapObject(JSContext* aCx,
 }
 
 bool WorkerNavigator::GlobalPrivacyControl() const {
+  if (auto value = MaskConfig::GetBool("navigator.globalPrivacyControl");
+      value.has_value())
+    return value.value();
   bool gpcStatus = StaticPrefs::privacy_globalprivacycontrol_enabled();
   if (!gpcStatus) {
     JSObject* jso = GetWrapper();
@@ -114,6 +118,8 @@ void WorkerNavigator::SetLanguages(const nsTArray<nsString>& aLanguages) {
 void WorkerNavigator::GetAppVersion(nsString& aAppVersion,
                                     CallerType aCallerType,
                                     ErrorResult& aRv) const {
+  if (auto value = MaskConfig::GetString("navigator.appVersion"))
+    return aAppVersion.Assign(NS_ConvertUTF8toUTF16(value.value()));
   WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
   MOZ_ASSERT(workerPrivate);
 
@@ -136,6 +142,8 @@ void WorkerNavigator::GetAppVersion(nsString& aAppVersion,
 
 void WorkerNavigator::GetPlatform(nsString& aPlatform, CallerType aCallerType,
                                   ErrorResult& aRv) const {
+  if (auto value = MaskConfig::GetString("navigator.platform"))
+    return aPlatform.Assign(NS_ConvertUTF8toUTF16(value.value()));
   WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
   MOZ_ASSERT(workerPrivate);
 
@@ -197,6 +205,8 @@ class GetUserAgentRunnable final : public WorkerMainThreadRunnable {
 
 void WorkerNavigator::GetUserAgent(nsString& aUserAgent, CallerType aCallerType,
                                    ErrorResult& aRv) const {
+  if (auto value = MaskConfig::GetString("navigator.userAgent"))
+    return aUserAgent.Assign(NS_ConvertUTF8toUTF16(value.value()));
   WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
   MOZ_ASSERT(workerPrivate);
 
@@ -208,6 +218,8 @@ void WorkerNavigator::GetUserAgent(nsString& aUserAgent, CallerType aCallerType,
 }
 
 uint64_t WorkerNavigator::HardwareConcurrency() const {
+  if (auto value = MaskConfig::GetUint64("navigator.hardwareConcurrency"))
+    return value.value();
   RuntimeService* rts = RuntimeService::GetService();
   MOZ_ASSERT(rts);
 
diff --git a/dom/workers/moz.build b/dom/workers/moz.build
index c7818826d1..0be0753e20 100644
--- a/dom/workers/moz.build
+++ b/dom/workers/moz.build
@@ -112,3 +112,6 @@ MARIONETTE_MANIFESTS += ["test/marionette/manifest.toml"]
 XPCSHELL_TESTS_MANIFESTS += ["test/xpcshell/xpcshell.toml"]
 
 BROWSER_CHROME_MANIFESTS += ["test/browser.toml"]
+
+# DOM Mask
+LOCAL_INCLUDES += ["/dom/mask"]
\ No newline at end of file