Adding upstream version 115.8.0esr.upstream/115.8.0esr

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

22 files changed, 5019 insertions, 0 deletions

diff --git a/toolkit/components/resistfingerprinting/KeyCodeConsensus_En_US.h b/toolkit/components/resistfingerprinting/KeyCodeConsensus_En_US.h
new file mode 100644
index 0000000000..a7956dbe1d
--- /dev/null
+++ b/toolkit/components/resistfingerprinting/KeyCodeConsensus_En_US.h
@@ -0,0 +1,174 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * 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/. */
+
+/**
+ * This file contains the spoofed keycodes of en-US for fingerprinting
+ * resistance. When privacy.resistFingerprinting is active, we spoof the user's
+ * keyboard layout according to the language of the document.
+ *
+ * Use CONTROL to define the control key.
+ *   CONTROL(keyNameIndex, codeNameIndex, keyCode)
+ *   @param keyNameIndex  The keyNameIndex of this control key.
+ *                        See KeyNameList.h for details.
+ *   @param codeNameIndex The codeNameIndex of this contorl key.
+ *                        See PhysicalKeyCodeNameList.h for details.
+ *   @param keyCode       The keyCode of this control key.
+ *                        See KeyEvent.webidl for details.
+ *
+ * Use KEY to define the key with its modifier states. The key will be spoofed
+ * with given modifier states.
+ *   KEY(keyString, codeNameIndex, keyCode, modifiers)
+ *   @param keyString     The key string of this key.
+ *   @param codeNameIndex The codeNameIndex of this key.
+ *                        See PhysicalKeyCodeNameList.h for details.
+ *   @param keyCode       The keyCode of this key.
+ *                        See KeyEvent.webidl for details.
+ *   @param modifiers     The spoofing modifier states for this key.
+ *                        See BasicEvents.h for details.
+ */
+
+/**
+ * Spoofed keycodes for English content (US English keyboard layout).
+ */
+
+// clang-format off
+CONTROL(Alt,         AltLeft,     dom::KeyboardEvent_Binding::DOM_VK_ALT)
+CONTROL(ArrowDown,   ArrowDown,   dom::KeyboardEvent_Binding::DOM_VK_DOWN)
+CONTROL(ArrowLeft,   ArrowLeft,   dom::KeyboardEvent_Binding::DOM_VK_LEFT)
+CONTROL(ArrowRight,  ArrowRight,  dom::KeyboardEvent_Binding::DOM_VK_RIGHT)
+CONTROL(ArrowUp,     ArrowUp,     dom::KeyboardEvent_Binding::DOM_VK_UP)
+CONTROL(Backspace,   Backspace,   dom::KeyboardEvent_Binding::DOM_VK_BACK_SPACE)
+CONTROL(CapsLock,    CapsLock,    dom::KeyboardEvent_Binding::DOM_VK_CAPS_LOCK)
+// Leaving "ContextMenu" key unimplemented; not every english keyboard has
+// this.  For example, MACOS doesn't have this.
+CONTROL(Control,     ControlLeft, dom::KeyboardEvent_Binding::DOM_VK_CONTROL)
+CONTROL(Delete,      Delete,      dom::KeyboardEvent_Binding::DOM_VK_DELETE)
+CONTROL(End,         End,         dom::KeyboardEvent_Binding::DOM_VK_END)
+CONTROL(Enter,       Enter,       dom::KeyboardEvent_Binding::DOM_VK_RETURN)
+CONTROL(Escape,      Escape,      dom::KeyboardEvent_Binding::DOM_VK_ESCAPE)
+// Leaving "Help" key unimplemented; it only appears in some keyboard in Linux.
+CONTROL(Home,        Home,        dom::KeyboardEvent_Binding::DOM_VK_HOME)
+CONTROL(Insert,      Insert,      dom::KeyboardEvent_Binding::DOM_VK_INSERT)
+CONTROL(Meta,        OSLeft,      dom::KeyboardEvent_Binding::DOM_VK_WIN)
+CONTROL(OS,          OSLeft,      dom::KeyboardEvent_Binding::DOM_VK_WIN)
+CONTROL(PageDown,    PageDown,    dom::KeyboardEvent_Binding::DOM_VK_PAGE_DOWN)
+CONTROL(PageUp,      PageUp,      dom::KeyboardEvent_Binding::DOM_VK_PAGE_UP)
+// Leaving "Pause", "PrintScreen" and "ScrollLock" keys unimplemented; they are
+// non-MACOS only.
+CONTROL(Shift,       ShiftLeft,   dom::KeyboardEvent_Binding::DOM_VK_SHIFT)
+CONTROL(Tab,         Tab,         dom::KeyboardEvent_Binding::DOM_VK_TAB)
+CONTROL(F1,          F1,          dom::KeyboardEvent_Binding::DOM_VK_F1)
+CONTROL(F2,          F2,          dom::KeyboardEvent_Binding::DOM_VK_F2)
+CONTROL(F3,          F3,          dom::KeyboardEvent_Binding::DOM_VK_F3)
+CONTROL(F4,          F4,          dom::KeyboardEvent_Binding::DOM_VK_F4)
+CONTROL(F5,          F5,          dom::KeyboardEvent_Binding::DOM_VK_F5)
+CONTROL(F6,          F6,          dom::KeyboardEvent_Binding::DOM_VK_F6)
+CONTROL(F7,          F7,          dom::KeyboardEvent_Binding::DOM_VK_F7)
+CONTROL(F8,          F8,          dom::KeyboardEvent_Binding::DOM_VK_F8)
+CONTROL(F9,          F9,          dom::KeyboardEvent_Binding::DOM_VK_F9)
+CONTROL(F10,         F10,         dom::KeyboardEvent_Binding::DOM_VK_F10)
+CONTROL(F11,         F11,         dom::KeyboardEvent_Binding::DOM_VK_F11)
+CONTROL(F12,         F12,         dom::KeyboardEvent_Binding::DOM_VK_F12)
+// Leaving "F13" to "F35" key unimplemented; they are some how platform
+// dependent.  "F13" to "F19" are on MAC's full keyboard but may not exist on
+// usual keyboard.  "F20" to "F24" are only available on Windows and Linux.
+// "F25" to "F35" are Linux only.  Leaving "Clear" key unimplemented; it's
+// inconsistent between platforms.
+KEY(" ",  Space,        dom::KeyboardEvent_Binding::DOM_VK_SPACE,  MODIFIER_NONE)
+KEY(",",  Comma,        dom::KeyboardEvent_Binding::DOM_VK_COMMA, MODIFIER_NONE)
+KEY("<",  Comma,        dom::KeyboardEvent_Binding::DOM_VK_COMMA, MODIFIER_SHIFT)
+KEY(".",  Period,       dom::KeyboardEvent_Binding::DOM_VK_PERIOD, MODIFIER_NONE)
+KEY(">",  Period,       dom::KeyboardEvent_Binding::DOM_VK_PERIOD, MODIFIER_SHIFT)
+KEY("/",  Slash,        dom::KeyboardEvent_Binding::DOM_VK_SLASH, MODIFIER_NONE)
+KEY("?",  Slash,        dom::KeyboardEvent_Binding::DOM_VK_SLASH, MODIFIER_SHIFT)
+KEY(";",  Semicolon,    dom::KeyboardEvent_Binding::DOM_VK_SEMICOLON,  MODIFIER_NONE)
+KEY(":",  Semicolon,    dom::KeyboardEvent_Binding::DOM_VK_SEMICOLON,  MODIFIER_SHIFT)
+KEY("'",  Quote,        dom::KeyboardEvent_Binding::DOM_VK_QUOTE, MODIFIER_NONE)
+KEY("\"", Quote,        dom::KeyboardEvent_Binding::DOM_VK_QUOTE, MODIFIER_SHIFT)
+KEY("[",  BracketLeft,  dom::KeyboardEvent_Binding::DOM_VK_OPEN_BRACKET, MODIFIER_NONE)
+KEY("{",  BracketLeft,  dom::KeyboardEvent_Binding::DOM_VK_OPEN_BRACKET, MODIFIER_SHIFT)
+KEY("]",  BracketRight, dom::KeyboardEvent_Binding::DOM_VK_CLOSE_BRACKET, MODIFIER_NONE)
+KEY("}",  BracketRight, dom::KeyboardEvent_Binding::DOM_VK_CLOSE_BRACKET, MODIFIER_SHIFT)
+KEY("`",  Backquote,    dom::KeyboardEvent_Binding::DOM_VK_BACK_QUOTE, MODIFIER_NONE)
+KEY("~",  Backquote,    dom::KeyboardEvent_Binding::DOM_VK_BACK_QUOTE, MODIFIER_SHIFT)
+KEY("\\", Backslash,    dom::KeyboardEvent_Binding::DOM_VK_BACK_SLASH, MODIFIER_NONE)
+KEY("|",  Backslash,    dom::KeyboardEvent_Binding::DOM_VK_BACK_SLASH, MODIFIER_SHIFT)
+KEY("-",  Minus,        dom::KeyboardEvent_Binding::DOM_VK_HYPHEN_MINUS, MODIFIER_NONE)
+KEY("_",  Minus,        dom::KeyboardEvent_Binding::DOM_VK_HYPHEN_MINUS, MODIFIER_SHIFT)
+KEY("=",  Equal,        dom::KeyboardEvent_Binding::DOM_VK_EQUALS, MODIFIER_NONE)
+KEY("+",  Equal,        dom::KeyboardEvent_Binding::DOM_VK_EQUALS, MODIFIER_SHIFT)
+KEY("A",  KeyA,         dom::KeyboardEvent_Binding::DOM_VK_A, MODIFIER_SHIFT)
+KEY("B",  KeyB,         dom::KeyboardEvent_Binding::DOM_VK_B, MODIFIER_SHIFT)
+KEY("C",  KeyC,         dom::KeyboardEvent_Binding::DOM_VK_C, MODIFIER_SHIFT)
+KEY("D",  KeyD,         dom::KeyboardEvent_Binding::DOM_VK_D, MODIFIER_SHIFT)
+KEY("E",  KeyE,         dom::KeyboardEvent_Binding::DOM_VK_E, MODIFIER_SHIFT)
+KEY("F",  KeyF,         dom::KeyboardEvent_Binding::DOM_VK_F, MODIFIER_SHIFT)
+KEY("G",  KeyG,         dom::KeyboardEvent_Binding::DOM_VK_G, MODIFIER_SHIFT)
+KEY("H",  KeyH,         dom::KeyboardEvent_Binding::DOM_VK_H, MODIFIER_SHIFT)
+KEY("I",  KeyI,         dom::KeyboardEvent_Binding::DOM_VK_I, MODIFIER_SHIFT)
+KEY("J",  KeyJ,         dom::KeyboardEvent_Binding::DOM_VK_J, MODIFIER_SHIFT)
+KEY("K",  KeyK,         dom::KeyboardEvent_Binding::DOM_VK_K, MODIFIER_SHIFT)
+KEY("L",  KeyL,         dom::KeyboardEvent_Binding::DOM_VK_L, MODIFIER_SHIFT)
+KEY("M",  KeyM,         dom::KeyboardEvent_Binding::DOM_VK_M, MODIFIER_SHIFT)
+KEY("N",  KeyN,         dom::KeyboardEvent_Binding::DOM_VK_N, MODIFIER_SHIFT)
+KEY("O",  KeyO,         dom::KeyboardEvent_Binding::DOM_VK_O, MODIFIER_SHIFT)
+KEY("P",  KeyP,         dom::KeyboardEvent_Binding::DOM_VK_P, MODIFIER_SHIFT)
+KEY("Q",  KeyQ,         dom::KeyboardEvent_Binding::DOM_VK_Q, MODIFIER_SHIFT)
+KEY("R",  KeyR,         dom::KeyboardEvent_Binding::DOM_VK_R, MODIFIER_SHIFT)
+KEY("S",  KeyS,         dom::KeyboardEvent_Binding::DOM_VK_S, MODIFIER_SHIFT)
+KEY("T",  KeyT,         dom::KeyboardEvent_Binding::DOM_VK_T, MODIFIER_SHIFT)
+KEY("U",  KeyU,         dom::KeyboardEvent_Binding::DOM_VK_U, MODIFIER_SHIFT)
+KEY("V",  KeyV,         dom::KeyboardEvent_Binding::DOM_VK_V, MODIFIER_SHIFT)
+KEY("W",  KeyW,         dom::KeyboardEvent_Binding::DOM_VK_W, MODIFIER_SHIFT)
+KEY("X",  KeyX,         dom::KeyboardEvent_Binding::DOM_VK_X, MODIFIER_SHIFT)
+KEY("Y",  KeyY,         dom::KeyboardEvent_Binding::DOM_VK_Y, MODIFIER_SHIFT)
+KEY("Z",  KeyZ,         dom::KeyboardEvent_Binding::DOM_VK_Z, MODIFIER_SHIFT)
+KEY("a",  KeyA,         dom::KeyboardEvent_Binding::DOM_VK_A, MODIFIER_NONE)
+KEY("b",  KeyB,         dom::KeyboardEvent_Binding::DOM_VK_B, MODIFIER_NONE)
+KEY("c",  KeyC,         dom::KeyboardEvent_Binding::DOM_VK_C, MODIFIER_NONE)
+KEY("d",  KeyD,         dom::KeyboardEvent_Binding::DOM_VK_D, MODIFIER_NONE)
+KEY("e",  KeyE,         dom::KeyboardEvent_Binding::DOM_VK_E, MODIFIER_NONE)
+KEY("f",  KeyF,         dom::KeyboardEvent_Binding::DOM_VK_F, MODIFIER_NONE)
+KEY("g",  KeyG,         dom::KeyboardEvent_Binding::DOM_VK_G, MODIFIER_NONE)
+KEY("h",  KeyH,         dom::KeyboardEvent_Binding::DOM_VK_H, MODIFIER_NONE)
+KEY("i",  KeyI,         dom::KeyboardEvent_Binding::DOM_VK_I, MODIFIER_NONE)
+KEY("j",  KeyJ,         dom::KeyboardEvent_Binding::DOM_VK_J, MODIFIER_NONE)
+KEY("k",  KeyK,         dom::KeyboardEvent_Binding::DOM_VK_K, MODIFIER_NONE)
+KEY("l",  KeyL,         dom::KeyboardEvent_Binding::DOM_VK_L, MODIFIER_NONE)
+KEY("m",  KeyM,         dom::KeyboardEvent_Binding::DOM_VK_M, MODIFIER_NONE)
+KEY("n",  KeyN,         dom::KeyboardEvent_Binding::DOM_VK_N, MODIFIER_NONE)
+KEY("o",  KeyO,         dom::KeyboardEvent_Binding::DOM_VK_O, MODIFIER_NONE)
+KEY("p",  KeyP,         dom::KeyboardEvent_Binding::DOM_VK_P, MODIFIER_NONE)
+KEY("q",  KeyQ,         dom::KeyboardEvent_Binding::DOM_VK_Q, MODIFIER_NONE)
+KEY("r",  KeyR,         dom::KeyboardEvent_Binding::DOM_VK_R, MODIFIER_NONE)
+KEY("s",  KeyS,         dom::KeyboardEvent_Binding::DOM_VK_S, MODIFIER_NONE)
+KEY("t",  KeyT,         dom::KeyboardEvent_Binding::DOM_VK_T, MODIFIER_NONE)
+KEY("u",  KeyU,         dom::KeyboardEvent_Binding::DOM_VK_U, MODIFIER_NONE)
+KEY("v",  KeyV,         dom::KeyboardEvent_Binding::DOM_VK_V, MODIFIER_NONE)
+KEY("w",  KeyW,         dom::KeyboardEvent_Binding::DOM_VK_W, MODIFIER_NONE)
+KEY("x",  KeyX,         dom::KeyboardEvent_Binding::DOM_VK_X, MODIFIER_NONE)
+KEY("y",  KeyY,         dom::KeyboardEvent_Binding::DOM_VK_Y, MODIFIER_NONE)
+KEY("z",  KeyZ,         dom::KeyboardEvent_Binding::DOM_VK_Z, MODIFIER_NONE)
+KEY("0",  Digit0,       dom::KeyboardEvent_Binding::DOM_VK_0, MODIFIER_NONE)
+KEY("1",  Digit1,       dom::KeyboardEvent_Binding::DOM_VK_1, MODIFIER_NONE)
+KEY("2",  Digit2,       dom::KeyboardEvent_Binding::DOM_VK_2, MODIFIER_NONE)
+KEY("3",  Digit3,       dom::KeyboardEvent_Binding::DOM_VK_3, MODIFIER_NONE)
+KEY("4",  Digit4,       dom::KeyboardEvent_Binding::DOM_VK_4, MODIFIER_NONE)
+KEY("5",  Digit5,       dom::KeyboardEvent_Binding::DOM_VK_5, MODIFIER_NONE)
+KEY("6",  Digit6,       dom::KeyboardEvent_Binding::DOM_VK_6, MODIFIER_NONE)
+KEY("7",  Digit7,       dom::KeyboardEvent_Binding::DOM_VK_7, MODIFIER_NONE)
+KEY("8",  Digit8,       dom::KeyboardEvent_Binding::DOM_VK_8, MODIFIER_NONE)
+KEY("9",  Digit9,       dom::KeyboardEvent_Binding::DOM_VK_9, MODIFIER_NONE)
+KEY(")",  Digit0,       dom::KeyboardEvent_Binding::DOM_VK_0, MODIFIER_SHIFT)
+KEY("!",  Digit1,       dom::KeyboardEvent_Binding::DOM_VK_1, MODIFIER_SHIFT)
+KEY("@",  Digit2,       dom::KeyboardEvent_Binding::DOM_VK_2, MODIFIER_SHIFT)
+KEY("#",  Digit3,       dom::KeyboardEvent_Binding::DOM_VK_3, MODIFIER_SHIFT)
+KEY("$",  Digit4,       dom::KeyboardEvent_Binding::DOM_VK_4, MODIFIER_SHIFT)
+KEY("%",  Digit5,       dom::KeyboardEvent_Binding::DOM_VK_5, MODIFIER_SHIFT)
+KEY("^",  Digit6,       dom::KeyboardEvent_Binding::DOM_VK_6, MODIFIER_SHIFT)
+KEY("&",  Digit7,       dom::KeyboardEvent_Binding::DOM_VK_7, MODIFIER_SHIFT)
+KEY("*",  Digit8,       dom::KeyboardEvent_Binding::DOM_VK_8, MODIFIER_SHIFT)
+KEY("(",  Digit9,       dom::KeyboardEvent_Binding::DOM_VK_9, MODIFIER_SHIFT)
+// clang-format on
diff --git a/toolkit/components/resistfingerprinting/RFPHelper.sys.mjs b/toolkit/components/resistfingerprinting/RFPHelper.sys.mjs
new file mode 100644
index 0000000000..d6d7a6eefe
--- /dev/null
+++ b/toolkit/components/resistfingerprinting/RFPHelper.sys.mjs
@@ -0,0 +1,642 @@
+// -*- indent-tabs-mode: nil; js-indent-level: 2 -*-
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * 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/. */
+
+import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs";
+
+const kPrefResistFingerprinting = "privacy.resistFingerprinting";
+const kPrefSpoofEnglish = "privacy.spoof_english";
+const kTopicHttpOnModifyRequest = "http-on-modify-request";
+
+const kPrefLetterboxing = "privacy.resistFingerprinting.letterboxing";
+const kPrefLetterboxingDimensions =
+  "privacy.resistFingerprinting.letterboxing.dimensions";
+const kPrefLetterboxingTesting =
+  "privacy.resistFingerprinting.letterboxing.testing";
+const kTopicDOMWindowOpened = "domwindowopened";
+
+var logConsole;
+function log(msg) {
+  if (!logConsole) {
+    logConsole = console.createInstance({
+      prefix: "RFPHelper.jsm",
+      maxLogLevelPref: "privacy.resistFingerprinting.jsmloglevel",
+    });
+  }
+
+  logConsole.log(msg);
+}
+
+class _RFPHelper {
+  // ============================================================================
+  // Shared Setup
+  // ============================================================================
+  constructor() {
+    this._initialized = false;
+  }
+
+  init() {
+    if (this._initialized) {
+      return;
+    }
+    this._initialized = true;
+
+    // Add unconditional observers
+    Services.prefs.addObserver(kPrefResistFingerprinting, this);
+    Services.prefs.addObserver(kPrefLetterboxing, this);
+    XPCOMUtils.defineLazyPreferenceGetter(
+      this,
+      "_letterboxingDimensions",
+      kPrefLetterboxingDimensions,
+      "",
+      null,
+      this._parseLetterboxingDimensions
+    );
+    XPCOMUtils.defineLazyPreferenceGetter(
+      this,
+      "_isLetterboxingTesting",
+      kPrefLetterboxingTesting,
+      false
+    );
+
+    // Add RFP and Letterboxing observers if prefs are enabled
+    this._handleResistFingerprintingChanged();
+    this._handleLetterboxingPrefChanged();
+  }
+
+  uninit() {
+    if (!this._initialized) {
+      return;
+    }
+    this._initialized = false;
+
+    // Remove unconditional observers
+    Services.prefs.removeObserver(kPrefResistFingerprinting, this);
+    Services.prefs.removeObserver(kPrefLetterboxing, this);
+    // Remove the RFP observers, swallowing exceptions if they weren't present
+    this._removeRFPObservers();
+  }
+
+  observe(subject, topic, data) {
+    switch (topic) {
+      case "nsPref:changed":
+        this._handlePrefChanged(data);
+        break;
+      case kTopicHttpOnModifyRequest:
+        this._handleHttpOnModifyRequest(subject, data);
+        break;
+      case kTopicDOMWindowOpened:
+        // We attach to the newly created window by adding tabsProgressListener
+        // and event listener on it. We listen for new tabs being added or
+        // the change of the content principal and apply margins accordingly.
+        this._handleDOMWindowOpened(subject);
+        break;
+      default:
+        break;
+    }
+  }
+
+  handleEvent(aMessage) {
+    switch (aMessage.type) {
+      case "TabOpen": {
+        let tab = aMessage.target;
+        this._addOrClearContentMargin(tab.linkedBrowser);
+        break;
+      }
+      default:
+        break;
+    }
+  }
+
+  _handlePrefChanged(data) {
+    switch (data) {
+      case kPrefResistFingerprinting:
+        this._handleResistFingerprintingChanged();
+        break;
+      case kPrefSpoofEnglish:
+        this._handleSpoofEnglishChanged();
+        break;
+      case kPrefLetterboxing:
+        this._handleLetterboxingPrefChanged();
+        break;
+      default:
+        break;
+    }
+  }
+
+  contentSizeUpdated(win) {
+    this._updateMarginsForTabsInWindow(win);
+  }
+
+  // ============================================================================
+  // Language Prompt
+  // ============================================================================
+  _addRFPObservers() {
+    Services.prefs.addObserver(kPrefSpoofEnglish, this);
+    if (this._shouldPromptForLanguagePref()) {
+      Services.obs.addObserver(this, kTopicHttpOnModifyRequest);
+    }
+  }
+
+  _removeRFPObservers() {
+    try {
+      Services.prefs.removeObserver(kPrefSpoofEnglish, this);
+    } catch (e) {
+      // do nothing
+    }
+    try {
+      Services.obs.removeObserver(this, kTopicHttpOnModifyRequest);
+    } catch (e) {
+      // do nothing
+    }
+  }
+
+  _handleResistFingerprintingChanged() {
+    if (Services.prefs.getBoolPref(kPrefResistFingerprinting)) {
+      this._addRFPObservers();
+    } else {
+      this._removeRFPObservers();
+    }
+  }
+
+  _handleSpoofEnglishChanged() {
+    switch (Services.prefs.getIntPref(kPrefSpoofEnglish)) {
+      case 0: // will prompt
+      // This should only happen when turning privacy.resistFingerprinting off.
+      // Works like disabling accept-language spoofing.
+      // fall through
+      case 1: // don't spoof
+        if (
+          Services.prefs.prefHasUserValue("javascript.use_us_english_locale")
+        ) {
+          Services.prefs.clearUserPref("javascript.use_us_english_locale");
+        }
+        // We don't reset intl.accept_languages. Instead, setting
+        // privacy.spoof_english to 1 allows user to change preferred language
+        // settings through Preferences UI.
+        break;
+      case 2: // spoof
+        Services.prefs.setCharPref("intl.accept_languages", "en-US, en");
+        Services.prefs.setBoolPref("javascript.use_us_english_locale", true);
+        break;
+      default:
+        break;
+    }
+  }
+
+  _shouldPromptForLanguagePref() {
+    return (
+      Services.locale.appLocaleAsBCP47.substr(0, 2) !== "en" &&
+      Services.prefs.getIntPref(kPrefSpoofEnglish) === 0
+    );
+  }
+
+  _handleHttpOnModifyRequest(subject, data) {
+    // If we are loading an HTTP page from content, show the
+    // "request English language web pages?" prompt.
+    let httpChannel = subject.QueryInterface(Ci.nsIHttpChannel);
+
+    let notificationCallbacks = httpChannel.notificationCallbacks;
+    if (!notificationCallbacks) {
+      return;
+    }
+
+    let loadContext = notificationCallbacks.getInterface(Ci.nsILoadContext);
+    if (!loadContext || !loadContext.isContent) {
+      return;
+    }
+
+    if (!subject.URI.schemeIs("http") && !subject.URI.schemeIs("https")) {
+      return;
+    }
+    // The above QI did not throw, the scheme is http[s], and we know the
+    // load context is content, so we must have a true HTTP request from content.
+    // Stop the observer and display the prompt if another window has
+    // not already done so.
+    Services.obs.removeObserver(this, kTopicHttpOnModifyRequest);
+
+    if (!this._shouldPromptForLanguagePref()) {
+      return;
+    }
+
+    this._promptForLanguagePreference();
+
+    // The Accept-Language header for this request was set when the
+    // channel was created. Reset it to match the value that will be
+    // used for future requests.
+    let val = this._getCurrentAcceptLanguageValue(subject.URI);
+    if (val) {
+      httpChannel.setRequestHeader("Accept-Language", val, false);
+    }
+  }
+
+  _promptForLanguagePreference() {
+    // Display two buttons, both with string titles.
+    let flags = Services.prompt.STD_YES_NO_BUTTONS;
+    let brandBundle = Services.strings.createBundle(
+      "chrome://branding/locale/brand.properties"
+    );
+    let brandShortName = brandBundle.GetStringFromName("brandShortName");
+    let navigatorBundle = Services.strings.createBundle(
+      "chrome://browser/locale/browser.properties"
+    );
+    let message = navigatorBundle.formatStringFromName(
+      "privacy.spoof_english",
+      [brandShortName]
+    );
+    let response = Services.prompt.confirmEx(
+      null,
+      "",
+      message,
+      flags,
+      null,
+      null,
+      null,
+      null,
+      { value: false }
+    );
+
+    // Update preferences to reflect their response and to prevent the prompt
+    // from being displayed again.
+    Services.prefs.setIntPref(kPrefSpoofEnglish, response == 0 ? 2 : 1);
+  }
+
+  _getCurrentAcceptLanguageValue(uri) {
+    let channel = Services.io.newChannelFromURI(
+      uri,
+      null, // aLoadingNode
+      Services.scriptSecurityManager.getSystemPrincipal(),
+      null, // aTriggeringPrincipal
+      Ci.nsILoadInfo.SEC_ALLOW_CROSS_ORIGIN_SEC_CONTEXT_IS_NULL,
+      Ci.nsIContentPolicy.TYPE_OTHER
+    );
+    let httpChannel;
+    try {
+      httpChannel = channel.QueryInterface(Ci.nsIHttpChannel);
+    } catch (e) {
+      return null;
+    }
+    return httpChannel.getRequestHeader("Accept-Language");
+  }
+
+  // ==============================================================================
+  // Letterboxing
+  // ============================================================================
+  /**
+   * We use the TabsProgressListener to catch the change of the content
+   * principal. We would clear the margins around the content viewport if
+   * it is the system principal.
+   */
+  onLocationChange(aBrowser) {
+    this._addOrClearContentMargin(aBrowser);
+  }
+
+  _handleLetterboxingPrefChanged() {
+    if (Services.prefs.getBoolPref(kPrefLetterboxing, false)) {
+      Services.ww.registerNotification(this);
+      this._registerActor();
+      this._attachAllWindows();
+    } else {
+      this._unregisterActor();
+      this._detachAllWindows();
+      Services.ww.unregisterNotification(this);
+    }
+  }
+
+  _registerActor() {
+    ChromeUtils.registerWindowActor("RFPHelper", {
+      parent: {
+        esModuleURI: "resource:///actors/RFPHelperParent.sys.mjs",
+      },
+      child: {
+        esModuleURI: "resource:///actors/RFPHelperChild.sys.mjs",
+        events: {
+          resize: {},
+        },
+      },
+      allFrames: true,
+    });
+  }
+
+  _unregisterActor() {
+    ChromeUtils.unregisterWindowActor("RFPHelper");
+  }
+
+  // The function to parse the dimension set from the pref value. The pref value
+  // should be formated as 'width1xheight1, width2xheight2, ...'. For
+  // example, '100x100, 200x200, 400x200 ...'.
+  _parseLetterboxingDimensions(aPrefValue) {
+    if (!aPrefValue || !aPrefValue.match(/^(?:\d+x\d+,\s*)*(?:\d+x\d+)$/)) {
+      if (aPrefValue) {
+        console.error(
+          `Invalid pref value for ${kPrefLetterboxingDimensions}: ${aPrefValue}`
+        );
+      }
+      return [];
+    }
+
+    return aPrefValue.split(",").map(item => {
+      let sizes = item.split("x").map(size => parseInt(size, 10));
+
+      return {
+        width: sizes[0],
+        height: sizes[1],
+      };
+    });
+  }
+
+  _addOrClearContentMargin(aBrowser) {
+    let tab = aBrowser.getTabBrowser().getTabForBrowser(aBrowser);
+
+    // We won't do anything for lazy browsers.
+    if (!aBrowser.isConnected) {
+      return;
+    }
+
+    // We should apply no margin around an empty tab or a tab with system
+    // principal.
+    if (tab.isEmpty || aBrowser.contentPrincipal.isSystemPrincipal) {
+      this._clearContentViewMargin(aBrowser);
+    } else {
+      this._roundContentView(aBrowser);
+    }
+  }
+
+  /**
+   * Given a width or height, returns the appropriate margin to apply.
+   */
+  steppedRange(aDimension) {
+    let stepping;
+    if (aDimension <= 50) {
+      return 0;
+    } else if (aDimension <= 500) {
+      stepping = 50;
+    } else if (aDimension <= 1600) {
+      stepping = 100;
+    } else {
+      stepping = 200;
+    }
+
+    return (aDimension % stepping) / 2;
+  }
+
+  /**
+   * The function will round the given browser by adding margins around the
+   * content viewport.
+   */
+  async _roundContentView(aBrowser) {
+    let logId = Math.random();
+    log("_roundContentView[" + logId + "]");
+    let win = aBrowser.ownerGlobal;
+    let browserContainer = aBrowser
+      .getTabBrowser()
+      .getBrowserContainer(aBrowser);
+
+    let { contentWidth, contentHeight, containerWidth, containerHeight } =
+      await win.promiseDocumentFlushed(() => {
+        let contentWidth = aBrowser.clientWidth;
+        let contentHeight = aBrowser.clientHeight;
+        let containerWidth = browserContainer.clientWidth;
+        let containerHeight = browserContainer.clientHeight;
+
+        // If the findbar or devtools are out, we need to subtract their height (plus 1
+        // for the separator) from the container height, because we need to adjust our
+        // letterboxing to account for it; however it is not included in that dimension
+        // (but rather is subtracted from the content height.)
+        let findBar = win.gFindBarInitialized ? win.gFindBar : undefined;
+        let findBarOffset =
+          findBar && !findBar.hidden ? findBar.clientHeight + 1 : 0;
+        let devtools = browserContainer.getElementsByClassName(
+          "devtools-toolbox-bottom-iframe"
+        );
+        let devtoolsOffset = devtools.length ? devtools[0].clientHeight : 0;
+
+        return {
+          contentWidth,
+          contentHeight,
+          containerWidth,
+          containerHeight: containerHeight - findBarOffset - devtoolsOffset,
+        };
+      });
+
+    log(
+      "_roundContentView[" +
+        logId +
+        "] contentWidth=" +
+        contentWidth +
+        " contentHeight=" +
+        contentHeight +
+        " containerWidth=" +
+        containerWidth +
+        " containerHeight=" +
+        containerHeight +
+        " "
+    );
+
+    let calcMargins = (aWidth, aHeight) => {
+      let result;
+      log(
+        "_roundContentView[" +
+          logId +
+          "] calcMargins(" +
+          aWidth +
+          ", " +
+          aHeight +
+          ")"
+      );
+      // If the set is empty, we will round the content with the default
+      // stepping size.
+      if (!this._letterboxingDimensions.length) {
+        result = {
+          width: this.steppedRange(aWidth),
+          height: this.steppedRange(aHeight),
+        };
+        log(
+          "_roundContentView[" +
+            logId +
+            "] calcMargins(" +
+            aWidth +
+            ", " +
+            aHeight +
+            ") = " +
+            result.width +
+            " x " +
+            result.height
+        );
+        return result;
+      }
+
+      let matchingArea = aWidth * aHeight;
+      let minWaste = Number.MAX_SAFE_INTEGER;
+      let targetDimensions = undefined;
+
+      // Find the desired dimensions which waste the least content area.
+      for (let dim of this._letterboxingDimensions) {
+        // We don't need to consider the dimensions which cannot fit into the
+        // real content size.
+        if (dim.width > aWidth || dim.height > aHeight) {
+          continue;
+        }
+
+        let waste = matchingArea - dim.width * dim.height;
+
+        if (waste >= 0 && waste < minWaste) {
+          targetDimensions = dim;
+          minWaste = waste;
+        }
+      }
+
+      // If we cannot find any dimensions match to the real content window, this
+      // means the content area is smaller the smallest size in the set. In this
+      // case, we won't apply any margins.
+      if (!targetDimensions) {
+        result = {
+          width: 0,
+          height: 0,
+        };
+      } else {
+        result = {
+          width: (aWidth - targetDimensions.width) / 2,
+          height: (aHeight - targetDimensions.height) / 2,
+        };
+      }
+
+      log(
+        "_roundContentView[" +
+          logId +
+          "] calcMargins(" +
+          aWidth +
+          ", " +
+          aHeight +
+          ") = " +
+          result.width +
+          " x " +
+          result.height
+      );
+      return result;
+    };
+
+    // Calculating the margins around the browser element in order to round the
+    // content viewport. We will use a 200x100 stepping if the dimension set
+    // is not given.
+    let margins = calcMargins(containerWidth, containerHeight);
+
+    // If the size of the content is already quantized, we do nothing.
+    if (aBrowser.style.margin == `${margins.height}px ${margins.width}px`) {
+      log("_roundContentView[" + logId + "] is_rounded == true");
+      if (this._isLetterboxingTesting) {
+        log(
+          "_roundContentView[" +
+            logId +
+            "] is_rounded == true test:letterboxing:update-margin-finish"
+        );
+        Services.obs.notifyObservers(
+          null,
+          "test:letterboxing:update-margin-finish"
+        );
+      }
+      return;
+    }
+
+    win.requestAnimationFrame(() => {
+      log(
+        "_roundContentView[" +
+          logId +
+          "] setting margins to " +
+          margins.width +
+          " x " +
+          margins.height
+      );
+      // One cannot (easily) control the color of a margin unfortunately.
+      // An initial attempt to use a border instead of a margin resulted
+      // in offset event dispatching; so for now we use a colorless margin.
+      aBrowser.style.margin = `${margins.height}px ${margins.width}px`;
+    });
+  }
+
+  _clearContentViewMargin(aBrowser) {
+    aBrowser.ownerGlobal.requestAnimationFrame(() => {
+      aBrowser.style.margin = "";
+    });
+  }
+
+  _updateMarginsForTabsInWindow(aWindow) {
+    let tabBrowser = aWindow.gBrowser;
+
+    for (let tab of tabBrowser.tabs) {
+      let browser = tab.linkedBrowser;
+      this._addOrClearContentMargin(browser);
+    }
+  }
+
+  _attachWindow(aWindow) {
+    aWindow.gBrowser.addTabsProgressListener(this);
+    aWindow.addEventListener("TabOpen", this);
+
+    // Rounding the content viewport.
+    this._updateMarginsForTabsInWindow(aWindow);
+  }
+
+  _attachAllWindows() {
+    let windowList = Services.wm.getEnumerator("navigator:browser");
+
+    while (windowList.hasMoreElements()) {
+      let win = windowList.getNext();
+
+      if (win.closed || !win.gBrowser) {
+        continue;
+      }
+
+      this._attachWindow(win);
+    }
+  }
+
+  _detachWindow(aWindow) {
+    let tabBrowser = aWindow.gBrowser;
+    tabBrowser.removeTabsProgressListener(this);
+    aWindow.removeEventListener("TabOpen", this);
+
+    // Clear all margins and tooltip for all browsers.
+    for (let tab of tabBrowser.tabs) {
+      let browser = tab.linkedBrowser;
+      this._clearContentViewMargin(browser);
+    }
+  }
+
+  _detachAllWindows() {
+    let windowList = Services.wm.getEnumerator("navigator:browser");
+
+    while (windowList.hasMoreElements()) {
+      let win = windowList.getNext();
+
+      if (win.closed || !win.gBrowser) {
+        continue;
+      }
+
+      this._detachWindow(win);
+    }
+  }
+
+  _handleDOMWindowOpened(win) {
+    let self = this;
+
+    win.addEventListener(
+      "load",
+      () => {
+        // We attach to the new window when it has been loaded if the new loaded
+        // window is a browsing window.
+        if (
+          win.document.documentElement.getAttribute("windowtype") !==
+          "navigator:browser"
+        ) {
+          return;
+        }
+        self._attachWindow(win);
+      },
+      { once: true }
+    );
+  }
+}
+
+export let RFPHelper = new _RFPHelper();
diff --git a/toolkit/components/resistfingerprinting/RFPTargets.inc b/toolkit/components/resistfingerprinting/RFPTargets.inc
new file mode 100644
index 0000000000..a65b52cba8
--- /dev/null
+++ b/toolkit/components/resistfingerprinting/RFPTargets.inc
@@ -0,0 +1,58 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * 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/. */
+
+// Names should not be re-used.
+
+ITEM_VALUE(TouchEvents,                 1u << 0)
+ITEM_VALUE(PointerEvents,               1u << 1)
+ITEM_VALUE(KeyboardEvents,              1u << 2)
+ITEM_VALUE(ScreenOrientation,           1u << 3)
+// SpeechSynthesis part of the Web Speech API
+ITEM_VALUE(SpeechSynthesis,             1u << 4)
+// `prefers-color-scheme` CSS media feature
+ITEM_VALUE(CSSPrefersColorScheme,       1u << 5)
+// `prefers-reduced-motion` CSS media feature
+ITEM_VALUE(CSSPrefersReducedMotion,     1u << 6)
+// `prefers-contrast` CSS media feature
+ITEM_VALUE(CSSPrefersContrast,          1u << 7)
+// Add random noises to image data extracted from canvas.
+ITEM_VALUE(CanvasRandomization,         1u << 8)
+// Canvas targets: For unusual combinations of these, see comments
+// in IsImageExtractionAllowed
+ITEM_VALUE(CanvasImageExtractionPrompt, 1u << 9)
+ITEM_VALUE(CanvasExtractionFromThirdPartiesIsBlocked, 1u << 10)
+ITEM_VALUE(CanvasExtractionBeforeUserInputIsBlocked, 1u << 11)
+// Various "client identification" values of the navigator object
+ITEM_VALUE(NavigatorAppName,            1u << 12)
+ITEM_VALUE(NavigatorAppVersion,         1u << 13)
+ITEM_VALUE(NavigatorBuildID,            1u << 14)
+ITEM_VALUE(NavigatorHWConcurrency,      1u << 15)
+ITEM_VALUE(NavigatorOscpu,              1u << 16)
+ITEM_VALUE(NavigatorPlatform,           1u << 17)
+ITEM_VALUE(NavigatorUserAgent,          1u << 18)
+// Audio/VideoStreamTrack labels
+ITEM_VALUE(StreamTrackLabel,            1u << 19)
+ITEM_VALUE(StreamVideoFacingMode,       1u << 20)
+
+// !!! Don't forget to update kDefaultFingerintingProtections in nsRFPService.cpp
+// if necessary.
+
+/*
+ * In certain cases, we precompute the value of ShouldRFP for e.g. a Document.
+ * (This saves us more computation and casting later.)  This document will still
+ * need to check whether an individual target is allowed, but the initial
+ * question of "Does this document have any RFP applied to it ever?" can still
+ * be precomputed. This enum value will always be included in RFPLite, so when a
+ * document asks if they might have RFP enabled, it will return true. (Putting
+ * this value in the overrides pref is undefined behavior and may do anything.)
+ */
+ITEM_VALUE(IsAlwaysEnabledForPrecompute, 0)
+
+/*
+ * This value is the default argument value, to allow all callsites to ShouldRFP
+ * continue working. We will eventually remove the default argument, and then also
+ * remove this enum value.
+ */
+ITEM_VALUE(Unknown, 0xffffffff)
diff --git a/toolkit/components/resistfingerprinting/RelativeTimeline.cpp b/toolkit/components/resistfingerprinting/RelativeTimeline.cpp
new file mode 100644
index 0000000000..eca7fca975
--- /dev/null
+++ b/toolkit/components/resistfingerprinting/RelativeTimeline.cpp
@@ -0,0 +1,39 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * 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 "nsCOMPtr.h"
+#include "nsIRandomGenerator.h"
+#include "nsServiceManagerUtils.h"
+
+#include "RelativeTimeline.h"
+
+namespace mozilla {
+
+int64_t RelativeTimeline::GetRandomTimelineSeed() {
+  if (mRandomTimelineSeed == 0) {
+    nsresult rv;
+    nsCOMPtr<nsIRandomGenerator> randomGenerator =
+        do_GetService("@mozilla.org/security/random-generator;1", &rv);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      mRandomTimelineSeed = rand();
+      return mRandomTimelineSeed;
+    }
+
+    uint8_t* buffer = nullptr;
+    rv = randomGenerator->GenerateRandomBytes(sizeof(mRandomTimelineSeed),
+                                              &buffer);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      mRandomTimelineSeed = rand();
+      return mRandomTimelineSeed;
+    }
+
+    memcpy(&mRandomTimelineSeed, buffer, sizeof(mRandomTimelineSeed));
+    MOZ_ASSERT(buffer);
+    free(buffer);
+  }
+  return mRandomTimelineSeed;
+}
+
+}  // namespace mozilla
diff --git a/toolkit/components/resistfingerprinting/RelativeTimeline.h b/toolkit/components/resistfingerprinting/RelativeTimeline.h
new file mode 100644
index 0000000000..bf23de904d
--- /dev/null
+++ b/toolkit/components/resistfingerprinting/RelativeTimeline.h
@@ -0,0 +1,25 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * 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/. */
+
+#ifndef __RelativeTimeline_h__
+#define __RelativeTimeline_h__
+
+#include <cstdint>
+
+namespace mozilla {
+
+class RelativeTimeline {
+ public:
+  RelativeTimeline() : mRandomTimelineSeed(0) {}
+
+  int64_t GetRandomTimelineSeed();
+
+ private:
+  uint64_t mRandomTimelineSeed;
+};
+
+}  // namespace mozilla
+
+#endif /* __RelativeTimeline_h__ */
diff --git a/toolkit/components/resistfingerprinting/docs/implementation.rst b/toolkit/components/resistfingerprinting/docs/implementation.rst
new file mode 100644
index 0000000000..9e8a7491d4
--- /dev/null
+++ b/toolkit/components/resistfingerprinting/docs/implementation.rst
@@ -0,0 +1,78 @@
+=========================
+Implementation
+=========================
+
+Checking if an object should resist fingerprinting is ideally done by referencing the `Document's ShouldResistFingerprinting <https://searchfox.org/mozilla-central/search?q=symbol:_ZNK7mozilla3dom8Document26ShouldResistFingerprintingENS_9RFPTargetE&redirect=false>`_ method.  This is both fast and correct.  In certain other situations, you may need to call some of the ``nsContentUtils::ShouldResistFingerprinting`` functions.  When doing so, you should avoid calling either of the functions marked *dangerous*.
+
+As you can see in the callgraph below, directly calling a *dangerous* function will skip some of the checks that occur further up-stack.
+
+.. mermaid::
+
+	graph TD
+	  SRFP["ShouldResistFingerprinting()"]
+	  click SRFP href "https://searchfox.org/mozilla-central/search?q=symbol:_ZN14nsContentUtils26ShouldResistFingerprintingEN7mozilla9RFPTargetE&redirect=false"
+
+	  SRGP_GO["ShouldResistFingerprinting(nsIGlobalObject* aGlobalObject"]
+	  click SRGP_GO href "https://searchfox.org/mozilla-central/search?q=symbol:_ZN14nsContentUtils26ShouldResistFingerprintingEP15nsIGlobalObjectN7mozilla9RFPTargetE&redirect=false"
+
+	  GO_SRFP["nsIGlobalObject*::ShouldResistFingerprinting()"]
+	  click GO_SRFP href "https://searchfox.org/mozilla-central/search?q=symbol:_ZNK15nsIGlobalObject26ShouldResistFingerprintingEN7mozilla9RFPTargetE&redirect=false"
+
+	  Doc_SRFP["Document::ShouldResistFingerprinting()<br />System Principal Check"]
+	  click Doc_SRFP href "https://searchfox.org/mozilla-central/search?q=symbol:_ZNK7mozilla3dom8Document26ShouldResistFingerprintingENS_9RFPTargetE&redirect=false"
+
+	  SRFP_char["ShouldResistFingerprinting(const char*)"]
+	  click SRFP_char href "https://searchfox.org/mozilla-central/search?q=symbol:_ZN14nsContentUtils26ShouldResistFingerprintingEPKcN7mozilla9RFPTargetE&redirect=false"
+
+	  SRFP_callertype_go["ShouldResistFingerprinting(CallerType, nsIGlobalObject*)<br />System Principal Check"]
+	  click SRFP_callertype_go href "https://searchfox.org/mozilla-central/search?q=symbol:_ZN14nsContentUtils26ShouldResistFingerprintingEN7mozilla3dom10CallerTypeEP15nsIGlobalObjectNS0_9RFPTargetE&redirect=false"
+
+	  SRFP_docshell["ShouldResistFingerprinting(nsIDocShell*)"]
+	  click SRFP_docshell href "https://searchfox.org/mozilla-central/search?q=symbol:_ZN14nsContentUtils26ShouldResistFingerprintingEP11nsIDocShellN7mozilla9RFPTargetE&redirect=false"
+
+	  SRFP_channel["ShouldResistFingerprinting(nsIChannel*)<br />ETPSaysShouldNotResistFingerprinting Check<br />CookieJarSettingsSaysShouldResistFingerprinting Check"]
+	  click SRFP_channel href "https://searchfox.org/mozilla-central/search?q=symbol:_ZN14nsContentUtils26ShouldResistFingerprintingEP10nsIChannelN7mozilla9RFPTargetE&redirect=false"
+
+	  SRFP_uri["ShouldResistFingerprinting_dangerous(nsIURI*, OriginAttributes)<br />PBM Check<br />Scheme (inc WebExtension) Check<br />About Page Check<br />URI & Partition Key Exempt Check"]
+	  click SRFP_uri href "https://searchfox.org/mozilla-central/search?q=symbol:_ZN14nsContentUtils36ShouldResistFingerprinting_dangerousEP6nsIURIRKN7mozilla16OriginAttributesEPKcNS2_9RFPTargetE&redirect=false"
+
+	  SRFP_principal["ShouldResistFingerprinting_dangerous(nsIPrincipal*)<br />System Principal Check<br />PBM Check<br />Scheme Check<br />About Page Check<br />Web Extension Principal Check<br />URI & Partition Key Exempt Check"]
+	  click SRFP_principal href "https://searchfox.org/mozilla-central/search?q=symbol:_ZN14nsContentUtils36ShouldResistFingerprinting_dangerousEP12nsIPrincipalPKcN7mozilla9RFPTargetE&redirect=false"
+
+
+
+
+	  SRFP_principal --> |null| SRFP_char
+
+	  SRFP_uri --> |null| SRFP_char
+
+	  SRFP_channel -->|null| SRFP_char
+	  SRFP_channel --> |Document Load| SRFP_uri
+	  SRFP_channel --> |Subresource Load| SRFP_principal
+
+	  SRFP_docshell -->|null| SRFP_char
+	  SRFP_docshell --> Doc_SRFP
+
+	  SRFP_callertype_go --> SRGP_GO
+	  SRFP_char --> SRFP
+	  SRGP_GO -->|null| SRFP_char
+	  SRGP_GO --> GO_SRFP
+
+	  GO_SRFP --> |innerWindow, outerWindow| Doc_SRFP
+	  Doc_SRFP --> SRFP_channel
+
+
+Exemptions and Targets
+~~~~~~~~~~~~~~~~~~~~~~
+
+Fingerprinting Resistance takes into account many things to determine if we should alter behavior:
+
+* Whether we are the System Principal
+* Whether we are a Web Extension
+* Whether Fingerprinting Resistance is applied to all browsing modes or only Private Browsing Mode
+* Whether the specific site you are visiting has been granted an exemption (taking into account the framing page)
+* Whether the specific **activity** is granted an exemption
+
+All callsites for ``ShouldResistFingerprinting`` take a (currently) optional ``RFPTarget`` value, which defaults to ``Unknown``.  While arguments such as ``Document`` or ``nsIChannel`` provide context for the first four exemptions above, the Target provides context for the final one.  A Target is a Web API or an activity - such as a Pointer Event, the Screen Orientation, or plugging a gamepad into your computer (and therefore producing a `gamepadconnected event <https://www.w3.org/TR/gamepad/#event-gamepadconnected>`_).  Most Targets correlate strongly to a specific Web API, but not all do: for example whether or not to automatically reject Canvas extraction requests from third parties is a separate Target from prompting to reject canvas extraction.
+
+In some situations we may *not* alter our behavior for a certain activity - this could be based on the fingerprinting resistance mode you are using, or per-site overrides to correct breakage.  Targets are defined `RFPTargets.inc <https://searchfox.org/mozilla-central/source/toolkit/components/resistfingerprinting/RFPTargets.inc>`_.
diff --git a/toolkit/components/resistfingerprinting/docs/index.rst b/toolkit/components/resistfingerprinting/docs/index.rst
new file mode 100644
index 0000000000..57bb24beac
--- /dev/null
+++ b/toolkit/components/resistfingerprinting/docs/index.rst
@@ -0,0 +1,8 @@
+=========================
+Fingerprinting Resistance
+=========================
+
+.. toctree::
+   :maxdepth: 1
+
+   implementation
diff --git a/toolkit/components/resistfingerprinting/moz.build b/toolkit/components/resistfingerprinting/moz.build
new file mode 100644
index 0000000000..550328165a
--- /dev/null
+++ b/toolkit/components/resistfingerprinting/moz.build
@@ -0,0 +1,28 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# 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/.
+
+with Files("**"):
+    BUG_COMPONENT = ("Core", "Privacy: Anti-Tracking")
+
+TEST_DIRS += ["tests"]
+
+UNIFIED_SOURCES += [
+    "nsRFPService.cpp",
+    "RelativeTimeline.cpp",
+]
+
+SPHINX_TREES["resistfingerprinting"] = "docs"
+
+FINAL_LIBRARY = "xul"
+
+EXPORTS += ["nsRFPService.h", "RFPTargets.inc"]
+EXPORTS.mozilla += [
+    "RelativeTimeline.h",
+]
+
+EXTRA_JS_MODULES += [
+    "RFPHelper.sys.mjs",
+]
diff --git a/toolkit/components/resistfingerprinting/nsRFPService.cpp b/toolkit/components/resistfingerprinting/nsRFPService.cpp
new file mode 100644
index 0000000000..42dca79e25
--- /dev/null
+++ b/toolkit/components/resistfingerprinting/nsRFPService.cpp
@@ -0,0 +1,1461 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * 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 "nsRFPService.h"
+
+#include <algorithm>
+#include <cfloat>
+#include <cinttypes>
+#include <cmath>
+#include <cstdlib>
+#include <cstring>
+#include <ctime>
+#include <new>
+#include <type_traits>
+#include <utility>
+
+#include "MainThreadUtils.h"
+#include "ScopedNSSTypes.h"
+
+#include "mozilla/ArrayIterator.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Atomics.h"
+#include "mozilla/Casting.h"
+#include "mozilla/ClearOnShutdown.h"
+#include "mozilla/HashFunctions.h"
+#include "mozilla/HelperMacros.h"
+#include "mozilla/Likely.h"
+#include "mozilla/Logging.h"
+#include "mozilla/MacroForEach.h"
+#include "mozilla/OriginAttributes.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/Services.h"
+#include "mozilla/StaticPrefs_javascript.h"
+#include "mozilla/StaticPrefs_network.h"
+#include "mozilla/StaticPrefs_privacy.h"
+#include "mozilla/StaticPtr.h"
+#include "mozilla/TextEvents.h"
+#include "mozilla/dom/Document.h"
+#include "mozilla/dom/Element.h"
+#include "mozilla/dom/KeyboardEventBinding.h"
+#include "mozilla/fallible.h"
+#include "mozilla/XorShift128PlusRNG.h"
+
+#include "nsBaseHashtable.h"
+#include "nsComponentManagerUtils.h"
+#include "nsCOMPtr.h"
+#include "nsContentUtils.h"
+#include "nsCoord.h"
+#include "nsTHashMap.h"
+#include "nsDebug.h"
+#include "nsError.h"
+#include "nsHashKeys.h"
+#include "nsJSUtils.h"
+#include "nsLiteralString.h"
+#include "nsPrintfCString.h"
+#include "nsServiceManagerUtils.h"
+#include "nsString.h"
+#include "nsStringFlags.h"
+#include "nsTArray.h"
+#include "nsTLiteralString.h"
+#include "nsTPromiseFlatString.h"
+#include "nsTStringRepr.h"
+#include "nsXPCOM.h"
+
+#include "nsICookieJarSettings.h"
+#include "nsICryptoHash.h"
+#include "nsIGlobalObject.h"
+#include "nsIObserverService.h"
+#include "nsIRandomGenerator.h"
+#include "nsIUserIdleService.h"
+#include "nsIXULAppInfo.h"
+
+#include "nscore.h"
+#include "prenv.h"
+#include "prtime.h"
+#include "xpcpublic.h"
+
+#include "js/Date.h"
+
+using namespace mozilla;
+
+static mozilla::LazyLogModule gResistFingerprintingLog(
+    "nsResistFingerprinting");
+
+#define RESIST_FINGERPRINTING_PREF "privacy.resistFingerprinting"
+#define RESIST_FINGERPRINTING_PBMODE_PREF "privacy.resistFingerprinting.pbmode"
+#define RESIST_FINGERPRINTINGPROTECTION_PREF "privacy.fingerprintingProtection"
+#define RESIST_FINGERPRINTINGPROTECTION_PBMODE_PREF \
+  "privacy.fingerprintingProtection.pbmode"
+#define RESIST_FINGERPRINTINGPROTECTION_OVERRIDE_PREF \
+  "privacy.fingerprintingProtection.overrides"
+#define RFP_TIMER_UNCONDITIONAL_VALUE 20
+#define PROFILE_INITIALIZED_TOPIC "profile-initial-state"
+#define LAST_PB_SESSION_EXITED_TOPIC "last-pb-context-exited"
+
+static constexpr uint32_t kVideoFramesPerSec = 30;
+static constexpr uint32_t kVideoDroppedRatio = 5;
+
+#define RFP_DEFAULT_SPOOFING_KEYBOARD_LANG KeyboardLang::EN
+#define RFP_DEFAULT_SPOOFING_KEYBOARD_REGION KeyboardRegion::US
+
+// Fingerprinting protections that are enabled by default. This can be
+// overridden using the privacy.fingerprintingProtection.overrides pref.
+const uint32_t kDefaultFingerintingProtections =
+    uint32_t(RFPTarget::CanvasRandomization);
+
+// ============================================================================
+// ============================================================================
+// ============================================================================
+// Structural Stuff & Pref Observing
+
+NS_IMPL_ISUPPORTS(nsRFPService, nsIObserver)
+
+static StaticRefPtr<nsRFPService> sRFPService;
+static bool sInitialized = false;
+
+// Actually enabled fingerprinting protections.
+static Atomic<uint32_t> sEnabledFingerintingProtections;
+
+/* static */
+nsRFPService* nsRFPService::GetOrCreate() {
+  if (!sInitialized) {
+    sRFPService = new nsRFPService();
+    nsresult rv = sRFPService->Init();
+
+    if (NS_FAILED(rv)) {
+      sRFPService = nullptr;
+      return nullptr;
+    }
+
+    ClearOnShutdown(&sRFPService);
+    sInitialized = true;
+  }
+
+  return sRFPService;
+}
+
+static const char* gCallbackPrefs[] = {
+    RESIST_FINGERPRINTING_PREF,
+    RESIST_FINGERPRINTING_PBMODE_PREF,
+    RESIST_FINGERPRINTINGPROTECTION_PREF,
+    RESIST_FINGERPRINTINGPROTECTION_PBMODE_PREF,
+    RESIST_FINGERPRINTINGPROTECTION_OVERRIDE_PREF,
+    nullptr,
+};
+
+nsresult nsRFPService::Init() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  nsresult rv;
+
+  nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+  NS_ENSURE_TRUE(obs, NS_ERROR_NOT_AVAILABLE);
+
+  rv = obs->AddObserver(this, NS_XPCOM_SHUTDOWN_OBSERVER_ID, false);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (XRE_IsParentProcess()) {
+    rv = obs->AddObserver(this, LAST_PB_SESSION_EXITED_TOPIC, false);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    rv = obs->AddObserver(this, OBSERVER_TOPIC_IDLE_DAILY, false);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+#if defined(XP_WIN)
+  rv = obs->AddObserver(this, PROFILE_INITIALIZED_TOPIC, false);
+  NS_ENSURE_SUCCESS(rv, rv);
+#endif
+
+  Preferences::RegisterCallbacks(nsRFPService::PrefChanged, gCallbackPrefs,
+                                 this);
+  // We backup the original TZ value here.
+  const char* tzValue = PR_GetEnv("TZ");
+  if (tzValue != nullptr) {
+    mInitialTZValue = nsCString(tzValue);
+  }
+
+  // Call Update here to cache the values of the prefs and set the timezone.
+  UpdateRFPPref();
+  UpdateFPPOverrideList();
+
+  return rv;
+}
+
+/* static */
+bool nsRFPService::IsRFPEnabledFor(RFPTarget aTarget) {
+  if (StaticPrefs::privacy_resistFingerprinting_DoNotUseDirectly() ||
+      StaticPrefs::privacy_resistFingerprinting_pbmode_DoNotUseDirectly()) {
+    return true;
+  }
+
+  if (StaticPrefs::privacy_fingerprintingProtection_DoNotUseDirectly() ||
+      StaticPrefs::privacy_fingerprintingProtection_pbmode_DoNotUseDirectly()) {
+    if (aTarget == RFPTarget::IsAlwaysEnabledForPrecompute) {
+      return true;
+    }
+    // All not yet explicitly defined targets are disabled by default (no
+    // fingerprinting protection).
+    if (aTarget == RFPTarget::Unknown) {
+      return false;
+    }
+    return sEnabledFingerintingProtections & uint32_t(aTarget);
+  }
+
+  return false;
+}
+
+// This function updates every fingerprinting item necessary except
+// timing-related
+void nsRFPService::UpdateRFPPref() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  bool resistFingerprinting = nsContentUtils::ShouldResistFingerprinting();
+
+  JS::SetReduceMicrosecondTimePrecisionCallback(
+      nsRFPService::ReduceTimePrecisionAsUSecsWrapper);
+
+  // The JavaScript engine can already set the timezone per realm/global,
+  // but we think there are still other users of libc that rely
+  // on the TZ environment variable.
+  if (!StaticPrefs::privacy_resistFingerprinting_testing_setTZtoUTC()) {
+    return;
+  }
+
+  if (resistFingerprinting) {
+    PR_SetEnv("TZ=UTC");
+  } else if (sInitialized) {
+    // We will not touch the TZ value if 'privacy.resistFingerprinting' is false
+    // during the time of initialization.
+    if (!mInitialTZValue.IsEmpty()) {
+      nsAutoCString tzValue = "TZ="_ns + mInitialTZValue;
+      static char* tz = nullptr;
+
+      // If the tz has been set before, we free it first since it will be
+      // allocated a new value later.
+      if (tz != nullptr) {
+        free(tz);
+      }
+      // PR_SetEnv() needs the input string been leaked intentionally, so
+      // we copy it here.
+      tz = ToNewCString(tzValue, mozilla::fallible);
+      if (tz != nullptr) {
+        PR_SetEnv(tz);
+      }
+    } else {
+#if defined(XP_WIN)
+      // For Windows, we reset the TZ to an empty string. This will make Windows
+      // to use its system timezone.
+      PR_SetEnv("TZ=");
+#else
+      // For POSIX like system, we reset the TZ to the /etc/localtime, which is
+      // the system timezone.
+      PR_SetEnv("TZ=:/etc/localtime");
+#endif
+    }
+  }
+
+  // If and only if the time zone was changed above, propagate the change to the
+  // <time.h> functions and the JS runtime.
+  if (resistFingerprinting || sInitialized) {
+    // localtime_r (and other functions) may not call tzset, so do this here
+    // after changing TZ to ensure all <time.h> functions use the new time zone.
+#if defined(XP_WIN)
+    _tzset();
+#else
+    tzset();
+#endif
+
+    nsJSUtils::ResetTimeZone();
+  }
+}
+
+void nsRFPService::UpdateFPPOverrideList() {
+  nsAutoString targetOverrides;
+  nsresult rv = Preferences::GetString(
+      RESIST_FINGERPRINTINGPROTECTION_OVERRIDE_PREF, targetOverrides);
+  if (!NS_SUCCEEDED(rv) || targetOverrides.IsEmpty()) {
+    MOZ_LOG(gResistFingerprintingLog, LogLevel::Warning,
+            ("Could not map any values"));
+    return;
+  }
+
+  uint32_t enabled = kDefaultFingerintingProtections;
+  for (const nsAString& each : targetOverrides.Split(',')) {
+    Maybe<RFPTarget> mappedValue =
+        nsRFPService::TextToRFPTarget(Substring(each, 1, each.Length() - 1));
+    if (mappedValue.isSome()) {
+      RFPTarget target = mappedValue.value();
+      if (target == RFPTarget::IsAlwaysEnabledForPrecompute ||
+          target == RFPTarget::Unknown) {
+        MOZ_LOG(gResistFingerprintingLog, LogLevel::Warning,
+                ("RFPTarget::%s is not a valid value",
+                 NS_ConvertUTF16toUTF8(each).get()));
+      } else if (each[0] == '+') {
+        enabled |= uint32_t(target);
+        MOZ_LOG(gResistFingerprintingLog, LogLevel::Warning,
+                ("Mapped value %s (0x%08x), to an addition, now we have 0x%08x",
+                 NS_ConvertUTF16toUTF8(each).get(), unsigned(target), enabled));
+      } else if (each[0] == '-') {
+        enabled &= ~uint32_t(target);
+        MOZ_LOG(
+            gResistFingerprintingLog, LogLevel::Warning,
+            ("Mapped value %s (0x%08x) to a subtraction, now we have 0x%08x",
+             NS_ConvertUTF16toUTF8(each).get(), unsigned(target), enabled));
+      } else {
+        MOZ_LOG(gResistFingerprintingLog, LogLevel::Warning,
+                ("Mapped value %s (0x%08x) to an RFPTarget Enum, but the first "
+                 "character wasn't + or -",
+                 NS_ConvertUTF16toUTF8(each).get(), unsigned(target)));
+      }
+    } else {
+      MOZ_LOG(gResistFingerprintingLog, LogLevel::Warning,
+              ("Could not map the value %s to an RFPTarget Enum",
+               NS_ConvertUTF16toUTF8(each).get()));
+    }
+  }
+
+  sEnabledFingerintingProtections = enabled;
+}
+
+/* static */
+Maybe<RFPTarget> nsRFPService::TextToRFPTarget(const nsAString& aText) {
+#define ITEM_VALUE(name, value)     \
+  if (aText.EqualsLiteral(#name)) { \
+    return Some(RFPTarget::name);   \
+  }
+
+#include "RFPTargets.inc"
+#undef ITEM_VALUE
+
+  return Nothing();
+}
+
+void nsRFPService::StartShutdown() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+
+  if (obs) {
+    obs->RemoveObserver(this, NS_XPCOM_SHUTDOWN_OBSERVER_ID);
+    if (XRE_IsParentProcess()) {
+      obs->RemoveObserver(this, LAST_PB_SESSION_EXITED_TOPIC);
+      obs->RemoveObserver(this, OBSERVER_TOPIC_IDLE_DAILY);
+    }
+  }
+
+  Preferences::UnregisterCallbacks(nsRFPService::PrefChanged, gCallbackPrefs,
+                                   this);
+}
+
+// static
+void nsRFPService::PrefChanged(const char* aPref, void* aSelf) {
+  static_cast<nsRFPService*>(aSelf)->PrefChanged(aPref);
+}
+
+void nsRFPService::PrefChanged(const char* aPref) {
+  nsDependentCString pref(aPref);
+
+  if (pref.EqualsLiteral(RESIST_FINGERPRINTINGPROTECTION_OVERRIDE_PREF)) {
+    UpdateFPPOverrideList();
+  } else {
+    UpdateRFPPref();
+
+#if defined(XP_WIN)
+    if (StaticPrefs::privacy_resistFingerprinting_testing_setTZtoUTC() &&
+        !XRE_IsE10sParentProcess()) {
+      // Windows does not follow POSIX. Updates to the TZ environment variable
+      // are not reflected immediately on that platform as they are on UNIX
+      // systems without this call.
+      _tzset();
+    }
+#endif
+  }
+}
+
+NS_IMETHODIMP
+nsRFPService::Observe(nsISupports* aObject, const char* aTopic,
+                      const char16_t* aMessage) {
+  if (strcmp(NS_XPCOM_SHUTDOWN_OBSERVER_ID, aTopic) == 0) {
+    StartShutdown();
+  }
+#if defined(XP_WIN)
+  else if (!strcmp(PROFILE_INITIALIZED_TOPIC, aTopic)) {
+    // If we're e10s, then we don't need to run this, since the child process
+    // will simply inherit the environment variable from the parent process, in
+    // which case it's unnecessary to call _tzset().
+    if (XRE_IsParentProcess() && !XRE_IsE10sParentProcess()) {
+      // Windows does not follow POSIX. Updates to the TZ environment variable
+      // are not reflected immediately on that platform as they are on UNIX
+      // systems without this call.
+      _tzset();
+    }
+
+    nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+    NS_ENSURE_TRUE(obs, NS_ERROR_NOT_AVAILABLE);
+
+    nsresult rv = obs->RemoveObserver(this, PROFILE_INITIALIZED_TOPIC);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+#endif
+
+  if (strcmp(LAST_PB_SESSION_EXITED_TOPIC, aTopic) == 0) {
+    // Clear the private session key when the private session ends so that we
+    // can generate a new key for the new private session.
+    ClearSessionKey(true);
+  }
+
+  if (!strcmp(OBSERVER_TOPIC_IDLE_DAILY, aTopic)) {
+    if (StaticPrefs::
+            privacy_resistFingerprinting_randomization_daily_reset_enabled()) {
+      ClearSessionKey(false);
+    }
+
+    if (StaticPrefs::
+            privacy_resistFingerprinting_randomization_daily_reset_private_enabled()) {
+      ClearSessionKey(true);
+    }
+  }
+
+  return NS_OK;
+}
+
+// ============================================================================
+// ============================================================================
+// ============================================================================
+// Reduce Timer Precision Stuff
+
+constexpr double RFP_TIME_ATOM_MS = 16.667;  // 60Hz, 1000/60 but rounded.
+/*
+In RFP RAF always runs at 60Hz, so we're ~0.02% off of 1000/60 here.
+```js
+extra_frames_per_frame = 16.667 / (1000/60) - 1 // 0.00028
+sec_per_extra_frame = 1 / (extra_frames_per_frame * 60) // 833.33
+min_per_extra_frame = sec_per_extra_frame / 60 // 13.89
+```
+We expect an extra frame every ~14 minutes, which is enough to be smooth.
+16.67 would be ~1.4 minutes, which is OK, but is more noticable.
+Put another way, if this is the only unacceptable hitch you have across 14
+minutes, I'm impressed, and we might revisit this.
+*/
+
+/* static */
+double nsRFPService::TimerResolution(RTPCallerType aRTPCallerType) {
+  double prefValue = StaticPrefs::
+      privacy_resistFingerprinting_reduceTimerPrecision_microseconds();
+  if (aRTPCallerType == RTPCallerType::ResistFingerprinting) {
+    return std::max(RFP_TIME_ATOM_MS * 1000.0, prefValue);
+  }
+  return prefValue;
+}
+
+/**
+ * The purpose of this function is to deterministicly generate a random midpoint
+ * between a lower clamped value and an upper clamped value. Assuming a clamping
+ * resolution of 100, here is an example:
+ *
+ * |---------------------------------------|--------------------------|
+ * lower clamped value (e.g. 300)          |           upper clamped value (400)
+ *                              random midpoint (e.g. 360)
+ *
+ * If our actual timestamp (e.g. 325) is below the midpoint, we keep it clamped
+ * downwards. If it were equal to or above the midpoint (e.g. 365) we would
+ * round it upwards to the largest clamped value (in this example: 400).
+ *
+ * The question is: does time go backwards?
+ *
+ * The midpoint is deterministicly random and generated from three components:
+ * a secret seed, a per-timeline (context) 'mix-in', and a clamped time.
+ *
+ * When comparing times across different seed values: time may go backwards.
+ * For a clamped time of 300, one seed may generate a midpoint of 305 and
+ * another 395. So comparing an (actual) timestamp of 325 and 351 could see the
+ * 325 clamped up to 400 and the 351 clamped down to 300. The seed is
+ * per-process, so this case occurs when one can compare timestamps
+ * cross-process. This is uncommon (because we don't have site isolation.) The
+ * circumstances this could occur are BroadcastChannel, Storage Notification,
+ * and in theory (but not yet implemented) SharedWorker. This should be an
+ * exhaustive list (at time of comment writing!).
+ *
+ * Aside from cross-process communication, derived timestamps across different
+ * time origins may go backwards. (Specifically, derived means adding two
+ * timestamps together to get an (approximate) absolute time.)
+ * Assume a page and a worker. If one calls performance.now() in the page and
+ * then triggers a call to performance.now() in the worker, the following
+ * invariant should hold true:
+ *             page.performance.timeOrigin + page.performance.now() <
+ *                      worker.performance.timeOrigin + worker.performance.now()
+ *
+ * We break this invariant.
+ *
+ * The 'Context Mix-in' is a securely generated random seed that is unique for
+ * each timeline that starts over at zero. It is needed to ensure that the
+ * sequence of midpoints (as calculated by the secret seed and clamped time)
+ * does not repeat. In RelativeTimeline.h, we define a 'RelativeTimeline' class
+ * that can be inherited by any object that has a relative timeline. The most
+ * obvious examples are Documents and Workers. An attacker could let time go
+ * forward and observe (roughly) where the random midpoints fall. Then they
+ * create a new object, time starts back over at zero, and they know
+ * (approximately) where the random midpoints are.
+ *
+ * When the timestamp given is a non-relative timestamp (e.g. it is relative to
+ * the unix epoch) it is not possible to replay a sequence of random values.
+ * Thus, providing a zero context pointer is an indicator that the timestamp
+ * given is absolute and does not need any additional randomness.
+ *
+ * @param aClampedTimeUSec [in]  The clamped input time in microseconds.
+ * @param aResolutionUSec  [in]  The current resolution for clamping in
+ *                               microseconds.
+ * @param aMidpointOut     [out] The midpoint, in microseconds, between [0,
+ *                               aResolutionUSec].
+ * @param aContextMixin    [in]  An opaque random value for relative
+ *                               timestamps. 0 for absolute timestamps
+ * @param aSecretSeed      [in]  TESTING ONLY. When provided, the current seed
+ *                               will be replaced with this value.
+ * @return                 A nsresult indicating success of failure. If the
+ *                         function failed, nothing is written to aMidpointOut
+ */
+
+/* static */
+nsresult nsRFPService::RandomMidpoint(long long aClampedTimeUSec,
+                                      long long aResolutionUSec,
+                                      int64_t aContextMixin,
+                                      long long* aMidpointOut,
+                                      uint8_t* aSecretSeed /* = nullptr */) {
+  nsresult rv;
+  const int kSeedSize = 16;
+  static Atomic<uint8_t*> sSecretMidpointSeed;
+
+  if (MOZ_UNLIKELY(!aMidpointOut)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  /*
+   * Below, we will use three different values to seed a fairly simple random
+   * number generator. On the first run we initiate the secret seed, which
+   * is mixed in with the time epoch and the context mix in to seed the RNG.
+   *
+   * This isn't the most secure method of generating a random midpoint but is
+   * reasonably performant and should be sufficient for our purposes.
+   */
+
+  // If we don't have a seed, we need to get one.
+  if (MOZ_UNLIKELY(!sSecretMidpointSeed)) {
+    nsCOMPtr<nsIRandomGenerator> randomGenerator =
+        do_GetService("@mozilla.org/security/random-generator;1", &rv);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    uint8_t* temp = nullptr;
+    rv = randomGenerator->GenerateRandomBytes(kSeedSize, &temp);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+    if (MOZ_UNLIKELY(!sSecretMidpointSeed.compareExchange(nullptr, temp))) {
+      // Some other thread initted this first, never mind!
+      delete[] temp;
+    }
+  }
+
+  // sSecretMidpointSeed is now set, and invariant. The contents of the buffer
+  // it points to is also invariant, _unless_ this function is called with a
+  // non-null |aSecretSeed|.
+  uint8_t* seed = sSecretMidpointSeed;
+  MOZ_RELEASE_ASSERT(seed);
+
+  // If someone has passed in the testing-only parameter, replace our seed with
+  // it. We do _not_ re-allocate the buffer, since that can lead to UAF below.
+  // The math could still be racy if the caller supplies a new secret seed while
+  // some other thread is calling this function, but since this is arcane
+  // test-only functionality that is used in only one test-case presently, we
+  // put the burden of using this particular footgun properly on the test code.
+  if (MOZ_UNLIKELY(aSecretSeed != nullptr)) {
+    memcpy(seed, aSecretSeed, kSeedSize);
+  }
+
+  // Seed and create our random number generator.
+  non_crypto::XorShift128PlusRNG rng(aContextMixin ^ *(uint64_t*)(seed),
+                                     aClampedTimeUSec ^ *(uint64_t*)(seed + 8));
+
+  // Retrieve the output midpoint value.
+  if (MOZ_UNLIKELY(aResolutionUSec <= 0)) {  // ??? Bug 1718066
+    return NS_ERROR_FAILURE;
+  }
+  *aMidpointOut = rng.next() % aResolutionUSec;
+
+  return NS_OK;
+}
+
+/**
+ * Given a precision value, this function will reduce a given input time to the
+ * nearest multiple of that precision.
+ *
+ * It will check if it is appropriate to clamp the input time according to the
+ * values of the given TimerPrecisionType.  Note that if one desires a minimum
+ * precision for Resist Fingerprinting, it is the caller's responsibility to
+ * provide the correct value. This means you should pass TimerResolution(),
+ * which enforces a minimum value on the precision based on preferences.
+ *
+ * It ensures the given precision value is greater than zero, if it is not it
+ * returns the input time.
+ *
+ * While the correct thing to pass is TimerResolution() we expose it as an
+ * argument for testing purposes only.
+ *
+ * @param aTime           [in] The input time to be clamped.
+ * @param aTimeScale      [in] The units the input time is in (Seconds,
+ *                             Milliseconds, or Microseconds).
+ * @param aResolutionUSec [in] The precision (in microseconds) to clamp to.
+ * @param aContextMixin   [in] An opaque random value for relative timestamps.
+ *                             0 for absolute timestamps
+ * @return                 If clamping is appropriate, the clamped value of the
+ *                         input, otherwise the input.
+ */
+/* static */
+double nsRFPService::ReduceTimePrecisionImpl(double aTime, TimeScale aTimeScale,
+                                             double aResolutionUSec,
+                                             int64_t aContextMixin,
+                                             TimerPrecisionType aType) {
+  if (aType == TimerPrecisionType::DangerouslyNone) {
+    return aTime;
+  }
+
+  // This boolean will serve as a flag indicating we are clamping the time
+  // unconditionally. We do this when timer reduction preference is off; but we
+  // still want to apply 20us clamping to al timestamps to avoid leaking
+  // nano-second precision.
+  bool unconditionalClamping = false;
+  if (aType == UnconditionalAKAHighRes || aResolutionUSec <= 0) {
+    unconditionalClamping = true;
+    aResolutionUSec = RFP_TIMER_UNCONDITIONAL_VALUE;  // 20 microseconds
+    aContextMixin = 0;  // Just clarifies our logging statement at the end,
+                        // otherwise unused
+  }
+
+  // Increase the time as needed until it is in microseconds.
+  // Note that a double can hold up to 2**53 with integer precision. This gives
+  // us only until June 5, 2255 in time-since-the-epoch with integer precision.
+  // So we will be losing microseconds precision after that date.
+  // We think this is okay, and we codify it in some tests.
+  double timeScaled = aTime * (1000000 / aTimeScale);
+  // Cut off anything less than a microsecond.
+  long long timeAsInt = timeScaled;
+
+  // If we have a blank context mixin, this indicates we (should) have an
+  // absolute timestamp. We check the time, and if it less than a unix timestamp
+  // about 10 years in the past, we output to the log and, in debug builds,
+  // assert. This is an error case we want to understand and fix: we must have
+  // given a relative timestamp with a mixin of 0 which is incorrect. Anyone
+  // running a debug build _probably_ has an accurate clock, and if they don't,
+  // they'll hopefully find this message and understand why things are crashing.
+  const long long kFeb282008 = 1204233985000;
+  if (aContextMixin == 0 && timeAsInt < kFeb282008 && !unconditionalClamping &&
+      aType != TimerPrecisionType::RFP) {
+    nsAutoCString type;
+    TypeToText(aType, type);
+    MOZ_LOG(
+        gResistFingerprintingLog, LogLevel::Error,
+        ("About to assert. aTime=%lli<%lli aContextMixin=%" PRId64 " aType=%s",
+         timeAsInt, kFeb282008, aContextMixin, type.get()));
+    MOZ_ASSERT(
+        false,
+        "ReduceTimePrecisionImpl was given a relative time "
+        "with an empty context mix-in (or your clock is 10+ years off.) "
+        "Run this with MOZ_LOG=nsResistFingerprinting:1 to get more details.");
+  }
+
+  // Cast the resolution (in microseconds) to an int.
+  long long resolutionAsInt = aResolutionUSec;
+  // Perform the clamping.
+  // We do a cast back to double to perform the division with doubles, then
+  // floor the result and the rest occurs with integer precision. This is
+  // because it gives consistency above and below zero. Above zero, performing
+  // the division in integers truncates decimals, taking the result closer to
+  // zero (a floor). Below zero, performing the division in integers truncates
+  // decimals, taking the result closer to zero (a ceil). The impact of this is
+  // that comparing two clamped values that should be related by a constant
+  // (e.g. 10s) that are across the zero barrier will no longer work. We need to
+  // round consistently towards positive infinity or negative infinity (we chose
+  // negative.) This can't be done with a truncation, it must be done with
+  // floor.
+  long long clamped =
+      floor(double(timeAsInt) / resolutionAsInt) * resolutionAsInt;
+
+  long long midpoint = 0;
+  long long clampedAndJittered = clamped;
+  if (!unconditionalClamping &&
+      StaticPrefs::privacy_resistFingerprinting_reduceTimerPrecision_jitter()) {
+    if (!NS_FAILED(RandomMidpoint(clamped, resolutionAsInt, aContextMixin,
+                                  &midpoint)) &&
+        timeAsInt >= clamped + midpoint) {
+      clampedAndJittered += resolutionAsInt;
+    }
+  }
+
+  // Cast it back to a double and reduce it to the correct units.
+  double ret = double(clampedAndJittered) / (1000000.0 / double(aTimeScale));
+
+  MOZ_LOG(
+      gResistFingerprintingLog, LogLevel::Verbose,
+      ("Given: (%.*f, Scaled: %.*f, Converted: %lli), Rounding %s with (%lli, "
+       "Originally %.*f), "
+       "Intermediate: (%lli), Clamped: (%lli) Jitter: (%i Context: %" PRId64
+       " Midpoint: %lli) "
+       "Final: (%lli Converted: %.*f)",
+       DBL_DIG - 1, aTime, DBL_DIG - 1, timeScaled, timeAsInt,
+       (unconditionalClamping ? "unconditionally" : "normally"),
+       resolutionAsInt, DBL_DIG - 1, aResolutionUSec,
+       (long long)floor(double(timeAsInt) / resolutionAsInt), clamped,
+       StaticPrefs::privacy_resistFingerprinting_reduceTimerPrecision_jitter(),
+       aContextMixin, midpoint, clampedAndJittered, DBL_DIG - 1, ret));
+
+  return ret;
+}
+
+/* static */
+double nsRFPService::ReduceTimePrecisionAsUSecs(double aTime,
+                                                int64_t aContextMixin,
+                                                RTPCallerType aRTPCallerType) {
+  const auto type = GetTimerPrecisionType(aRTPCallerType);
+  return nsRFPService::ReduceTimePrecisionImpl(aTime, MicroSeconds,
+                                               TimerResolution(aRTPCallerType),
+                                               aContextMixin, type);
+}
+
+/* static */
+double nsRFPService::ReduceTimePrecisionAsMSecs(double aTime,
+                                                int64_t aContextMixin,
+                                                RTPCallerType aRTPCallerType) {
+  const auto type = GetTimerPrecisionType(aRTPCallerType);
+  return nsRFPService::ReduceTimePrecisionImpl(aTime, MilliSeconds,
+                                               TimerResolution(aRTPCallerType),
+                                               aContextMixin, type);
+}
+
+/* static */
+double nsRFPService::ReduceTimePrecisionAsMSecsRFPOnly(
+    double aTime, int64_t aContextMixin, RTPCallerType aRTPCallerType) {
+  return nsRFPService::ReduceTimePrecisionImpl(
+      aTime, MilliSeconds, TimerResolution(aRTPCallerType), aContextMixin,
+      GetTimerPrecisionTypeRFPOnly(aRTPCallerType));
+}
+
+/* static */
+double nsRFPService::ReduceTimePrecisionAsSecs(double aTime,
+                                               int64_t aContextMixin,
+                                               RTPCallerType aRTPCallerType) {
+  const auto type = GetTimerPrecisionType(aRTPCallerType);
+  return nsRFPService::ReduceTimePrecisionImpl(
+      aTime, Seconds, TimerResolution(aRTPCallerType), aContextMixin, type);
+}
+
+/* static */
+double nsRFPService::ReduceTimePrecisionAsSecsRFPOnly(
+    double aTime, int64_t aContextMixin, RTPCallerType aRTPCallerType) {
+  return nsRFPService::ReduceTimePrecisionImpl(
+      aTime, Seconds, TimerResolution(aRTPCallerType), aContextMixin,
+      GetTimerPrecisionTypeRFPOnly(aRTPCallerType));
+}
+
+/* static */
+double nsRFPService::ReduceTimePrecisionAsUSecsWrapper(
+    double aTime, bool aShouldResistFingerprinting, JSContext* aCx) {
+  MOZ_ASSERT(aCx);
+
+  nsCOMPtr<nsIGlobalObject> global = xpc::CurrentNativeGlobal(aCx);
+  MOZ_ASSERT(global);
+
+  RTPCallerType callerType;
+  if (aShouldResistFingerprinting) {
+    callerType = RTPCallerType::ResistFingerprinting;
+  } else if (global->CrossOriginIsolated()) {
+    callerType = RTPCallerType::CrossOriginIsolated;
+  } else {
+    callerType = RTPCallerType::Normal;
+  }
+  return nsRFPService::ReduceTimePrecisionImpl(
+      aTime, MicroSeconds, TimerResolution(callerType),
+      0, /* For absolute timestamps (all the JS engine does), supply zero
+            context mixin */
+      GetTimerPrecisionType(callerType));
+}
+
+/* static */
+TimerPrecisionType nsRFPService::GetTimerPrecisionType(
+    RTPCallerType aRTPCallerType) {
+  if (aRTPCallerType == RTPCallerType::SystemPrincipal) {
+    return DangerouslyNone;
+  }
+
+  if (aRTPCallerType == RTPCallerType::ResistFingerprinting) {
+    return RFP;
+  }
+
+  if (StaticPrefs::privacy_reduceTimerPrecision() &&
+      aRTPCallerType == RTPCallerType::CrossOriginIsolated) {
+    return UnconditionalAKAHighRes;
+  }
+
+  if (StaticPrefs::privacy_reduceTimerPrecision()) {
+    return Normal;
+  }
+
+  if (StaticPrefs::privacy_reduceTimerPrecision_unconditional()) {
+    return UnconditionalAKAHighRes;
+  }
+
+  return DangerouslyNone;
+}
+
+/* static */
+TimerPrecisionType nsRFPService::GetTimerPrecisionTypeRFPOnly(
+    RTPCallerType aRTPCallerType) {
+  if (aRTPCallerType == RTPCallerType::ResistFingerprinting) {
+    return RFP;
+  }
+
+  if (StaticPrefs::privacy_reduceTimerPrecision_unconditional() &&
+      aRTPCallerType != RTPCallerType::SystemPrincipal) {
+    return UnconditionalAKAHighRes;
+  }
+
+  return DangerouslyNone;
+}
+
+/* static */
+void nsRFPService::TypeToText(TimerPrecisionType aType, nsACString& aText) {
+  switch (aType) {
+    case TimerPrecisionType::DangerouslyNone:
+      aText.AssignLiteral("DangerouslyNone");
+      return;
+    case TimerPrecisionType::Normal:
+      aText.AssignLiteral("Normal");
+      return;
+    case TimerPrecisionType::RFP:
+      aText.AssignLiteral("RFP");
+      return;
+    case TimerPrecisionType::UnconditionalAKAHighRes:
+      aText.AssignLiteral("UnconditionalAKAHighRes");
+      return;
+    default:
+      MOZ_ASSERT(false, "Shouldn't go here");
+      aText.AssignLiteral("Unknown Enum Value");
+      return;
+  }
+}
+
+// ============================================================================
+// ============================================================================
+// ============================================================================
+// Video Statistics Spoofing
+
+/* static */
+uint32_t nsRFPService::CalculateTargetVideoResolution(uint32_t aVideoQuality) {
+  return aVideoQuality * NSToIntCeil(aVideoQuality * 16 / 9.0);
+}
+
+/* static */
+uint32_t nsRFPService::GetSpoofedTotalFrames(double aTime) {
+  double precision =
+      TimerResolution(RTPCallerType::ResistFingerprinting) / 1000 / 1000;
+  double time = floor(aTime / precision) * precision;
+
+  return NSToIntFloor(time * kVideoFramesPerSec);
+}
+
+/* static */
+uint32_t nsRFPService::GetSpoofedDroppedFrames(double aTime, uint32_t aWidth,
+                                               uint32_t aHeight) {
+  uint32_t targetRes = CalculateTargetVideoResolution(
+      StaticPrefs::privacy_resistFingerprinting_target_video_res());
+
+  // The video resolution is less than or equal to the target resolution, we
+  // report a zero dropped rate for this case.
+  if (targetRes >= aWidth * aHeight) {
+    return 0;
+  }
+
+  double precision =
+      TimerResolution(RTPCallerType::ResistFingerprinting) / 1000 / 1000;
+  double time = floor(aTime / precision) * precision;
+  // Bound the dropped ratio from 0 to 100.
+  uint32_t boundedDroppedRatio = std::min(kVideoDroppedRatio, 100U);
+
+  return NSToIntFloor(time * kVideoFramesPerSec *
+                      (boundedDroppedRatio / 100.0));
+}
+
+/* static */
+uint32_t nsRFPService::GetSpoofedPresentedFrames(double aTime, uint32_t aWidth,
+                                                 uint32_t aHeight) {
+  uint32_t targetRes = CalculateTargetVideoResolution(
+      StaticPrefs::privacy_resistFingerprinting_target_video_res());
+
+  // The target resolution is greater than the current resolution. For this
+  // case, there will be no dropped frames, so we report total frames directly.
+  if (targetRes >= aWidth * aHeight) {
+    return GetSpoofedTotalFrames(aTime);
+  }
+
+  double precision =
+      TimerResolution(RTPCallerType::ResistFingerprinting) / 1000 / 1000;
+  double time = floor(aTime / precision) * precision;
+  // Bound the dropped ratio from 0 to 100.
+  uint32_t boundedDroppedRatio = std::min(kVideoDroppedRatio, 100U);
+
+  return NSToIntFloor(time * kVideoFramesPerSec *
+                      ((100 - boundedDroppedRatio) / 100.0));
+}
+
+// ============================================================================
+// ============================================================================
+// ============================================================================
+// User-Agent/Version Stuff
+
+static const char* GetSpoofedVersion() {
+#ifdef ANDROID
+  // Return Desktop's ESR version.
+  // When Android RFP returns an ESR version >= 120, we can remove the "rv:109"
+  // spoofing in GetSpoofedUserAgent() below and stop #including
+  // StaticPrefs_network.h.
+  return "115.0";
+#else
+  return MOZILLA_UAVERSION;
+#endif
+}
+
+/* static */
+void nsRFPService::GetSpoofedUserAgent(nsACString& userAgent,
+                                       bool isForHTTPHeader) {
+  // This function generates the spoofed value of User Agent.
+  // We spoof the values of the platform and Firefox version, which could be
+  // used as fingerprinting sources to identify individuals.
+  // Reference of the format of User Agent:
+  // https://developer.mozilla.org/en-US/docs/Web/API/NavigatorID/userAgent
+  // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/User-Agent
+
+  // These magic numbers are the lengths of the UA string literals below.
+  // Assume three-digit Firefox version numbers so we have room to grow.
+  size_t preallocatedLength =
+      13 +
+      (isForHTTPHeader ? mozilla::ArrayLength(SPOOFED_HTTP_UA_OS)
+                       : mozilla::ArrayLength(SPOOFED_UA_OS)) -
+      1 + 5 + 3 + 10 + mozilla::ArrayLength(LEGACY_UA_GECKO_TRAIL) - 1 + 9 + 3 +
+      2;
+  userAgent.SetCapacity(preallocatedLength);
+
+  const char* spoofedVersion = GetSpoofedVersion();
+
+  // "Mozilla/5.0 (%s; rv:%d.0) Gecko/%d Firefox/%d.0"
+  userAgent.AssignLiteral("Mozilla/5.0 (");
+
+  if (isForHTTPHeader) {
+    userAgent.AppendLiteral(SPOOFED_HTTP_UA_OS);
+  } else {
+    userAgent.AppendLiteral(SPOOFED_UA_OS);
+  }
+
+  userAgent.AppendLiteral("; rv:");
+
+  // Desktop Firefox (regular and RFP) won't need to spoof "rv:109" in versions
+  // >= 120 (bug 1806690), but Android RFP will need to continue spoofing 109
+  // as long as Android's GetSpoofedVersion() returns a version < 120 above.
+  uint32_t forceRV = mozilla::StaticPrefs::network_http_useragent_forceRVOnly();
+  if (forceRV) {
+    userAgent.Append(nsPrintfCString("%u.0", forceRV));
+  } else {
+    userAgent.Append(spoofedVersion);
+  }
+
+  userAgent.AppendLiteral(") Gecko/");
+
+#if defined(ANDROID)
+  userAgent.Append(spoofedVersion);
+#else
+  userAgent.AppendLiteral(LEGACY_UA_GECKO_TRAIL);
+#endif
+
+  userAgent.AppendLiteral(" Firefox/");
+  userAgent.Append(spoofedVersion);
+
+  MOZ_ASSERT(userAgent.Length() <= preallocatedLength);
+}
+
+// ============================================================================
+// ============================================================================
+// ============================================================================
+// Keyboard Spoofing Stuff
+
+nsTHashMap<KeyboardHashKey, const SpoofingKeyboardCode*>*
+    nsRFPService::sSpoofingKeyboardCodes = nullptr;
+
+KeyboardHashKey::KeyboardHashKey(const KeyboardLangs aLang,
+                                 const KeyboardRegions aRegion,
+                                 const KeyNameIndexType aKeyIdx,
+                                 const nsAString& aKey)
+    : mLang(aLang), mRegion(aRegion), mKeyIdx(aKeyIdx), mKey(aKey) {}
+
+KeyboardHashKey::KeyboardHashKey(KeyTypePointer aOther)
+    : mLang(aOther->mLang),
+      mRegion(aOther->mRegion),
+      mKeyIdx(aOther->mKeyIdx),
+      mKey(aOther->mKey) {}
+
+KeyboardHashKey::KeyboardHashKey(KeyboardHashKey&& aOther) noexcept
+    : PLDHashEntryHdr(std::move(aOther)),
+      mLang(std::move(aOther.mLang)),
+      mRegion(std::move(aOther.mRegion)),
+      mKeyIdx(std::move(aOther.mKeyIdx)),
+      mKey(std::move(aOther.mKey)) {}
+
+KeyboardHashKey::~KeyboardHashKey() = default;
+
+bool KeyboardHashKey::KeyEquals(KeyTypePointer aOther) const {
+  return mLang == aOther->mLang && mRegion == aOther->mRegion &&
+         mKeyIdx == aOther->mKeyIdx && mKey == aOther->mKey;
+}
+
+KeyboardHashKey::KeyTypePointer KeyboardHashKey::KeyToPointer(KeyType aKey) {
+  return &aKey;
+}
+
+PLDHashNumber KeyboardHashKey::HashKey(KeyTypePointer aKey) {
+  PLDHashNumber hash = mozilla::HashString(aKey->mKey);
+  return mozilla::AddToHash(hash, aKey->mRegion, aKey->mKeyIdx, aKey->mLang);
+}
+
+/* static */
+void nsRFPService::MaybeCreateSpoofingKeyCodes(const KeyboardLangs aLang,
+                                               const KeyboardRegions aRegion) {
+  if (sSpoofingKeyboardCodes == nullptr) {
+    sSpoofingKeyboardCodes =
+        new nsTHashMap<KeyboardHashKey, const SpoofingKeyboardCode*>();
+  }
+
+  if (KeyboardLang::EN == aLang) {
+    switch (aRegion) {
+      case KeyboardRegion::US:
+        MaybeCreateSpoofingKeyCodesForEnUS();
+        break;
+    }
+  }
+}
+
+/* static */
+void nsRFPService::MaybeCreateSpoofingKeyCodesForEnUS() {
+  MOZ_ASSERT(sSpoofingKeyboardCodes);
+
+  static bool sInitialized = false;
+  const KeyboardLangs lang = KeyboardLang::EN;
+  const KeyboardRegions reg = KeyboardRegion::US;
+
+  if (sInitialized) {
+    return;
+  }
+
+  static const SpoofingKeyboardInfo spoofingKeyboardInfoTable[] = {
+#define KEY(key_, _codeNameIdx, _keyCode, _modifier) \
+  {NS_LITERAL_STRING_FROM_CSTRING(key_),             \
+   KEY_NAME_INDEX_USE_STRING,                        \
+   {CODE_NAME_INDEX_##_codeNameIdx, _keyCode, _modifier}},
+#define CONTROL(keyNameIdx_, _codeNameIdx, _keyCode) \
+  {u""_ns,                                           \
+   KEY_NAME_INDEX_##keyNameIdx_,                     \
+   {CODE_NAME_INDEX_##_codeNameIdx, _keyCode, MODIFIER_NONE}},
+#include "KeyCodeConsensus_En_US.h"
+#undef CONTROL
+#undef KEY
+  };
+
+  for (const auto& keyboardInfo : spoofingKeyboardInfoTable) {
+    KeyboardHashKey key(lang, reg, keyboardInfo.mKeyIdx, keyboardInfo.mKey);
+    MOZ_ASSERT(!sSpoofingKeyboardCodes->Contains(key),
+               "Double-defining key code; fix your KeyCodeConsensus file");
+    sSpoofingKeyboardCodes->InsertOrUpdate(key, &keyboardInfo.mSpoofingCode);
+  }
+
+  sInitialized = true;
+}
+
+/* static */
+void nsRFPService::GetKeyboardLangAndRegion(const nsAString& aLanguage,
+                                            KeyboardLangs& aLocale,
+                                            KeyboardRegions& aRegion) {
+  nsAutoString langStr;
+  nsAutoString regionStr;
+  uint32_t partNum = 0;
+
+  for (const nsAString& part : aLanguage.Split('-')) {
+    if (partNum == 0) {
+      langStr = part;
+    } else {
+      regionStr = part;
+      break;
+    }
+
+    partNum++;
+  }
+
+  // We test each language here as well as the region. There are some cases that
+  // only the language is given, we will use the default region code when this
+  // happens. The default region should depend on the given language.
+  if (langStr.EqualsLiteral(RFP_KEYBOARD_LANG_STRING_EN)) {
+    aLocale = KeyboardLang::EN;
+    // Give default values first.
+    aRegion = KeyboardRegion::US;
+
+    if (regionStr.EqualsLiteral(RFP_KEYBOARD_REGION_STRING_US)) {
+      aRegion = KeyboardRegion::US;
+    }
+  } else {
+    // There is no spoofed keyboard locale for the given language. We use the
+    // default one in this case.
+    aLocale = RFP_DEFAULT_SPOOFING_KEYBOARD_LANG;
+    aRegion = RFP_DEFAULT_SPOOFING_KEYBOARD_REGION;
+  }
+}
+
+/* static */
+bool nsRFPService::GetSpoofedKeyCodeInfo(
+    const dom::Document* aDoc, const WidgetKeyboardEvent* aKeyboardEvent,
+    SpoofingKeyboardCode& aOut) {
+  MOZ_ASSERT(aKeyboardEvent);
+
+  KeyboardLangs keyboardLang = RFP_DEFAULT_SPOOFING_KEYBOARD_LANG;
+  KeyboardRegions keyboardRegion = RFP_DEFAULT_SPOOFING_KEYBOARD_REGION;
+  // If the document is given, we use the content language which is get from the
+  // document. Otherwise, we use the default one.
+  if (aDoc != nullptr) {
+    nsAutoString language;
+    aDoc->GetContentLanguage(language);
+
+    // If the content-langauge is not given, we try to get langauge from the
+    // HTML lang attribute.
+    if (language.IsEmpty()) {
+      dom::Element* elm = aDoc->GetHtmlElement();
+
+      if (elm != nullptr) {
+        elm->GetLang(language);
+      }
+    }
+
+    // If two or more languages are given, per HTML5 spec, we should consider
+    // it as 'unknown'. So we use the default one.
+    if (!language.IsEmpty() && !language.Contains(char16_t(','))) {
+      language.StripWhitespace();
+      GetKeyboardLangAndRegion(language, keyboardLang, keyboardRegion);
+    }
+  }
+
+  MaybeCreateSpoofingKeyCodes(keyboardLang, keyboardRegion);
+
+  KeyNameIndex keyIdx = aKeyboardEvent->mKeyNameIndex;
+  nsAutoString keyName;
+
+  if (keyIdx == KEY_NAME_INDEX_USE_STRING) {
+    keyName = aKeyboardEvent->mKeyValue;
+  }
+
+  KeyboardHashKey key(keyboardLang, keyboardRegion, keyIdx, keyName);
+  const SpoofingKeyboardCode* keyboardCode = sSpoofingKeyboardCodes->Get(key);
+
+  if (keyboardCode != nullptr) {
+    aOut = *keyboardCode;
+    return true;
+  }
+
+  return false;
+}
+
+/* static */
+bool nsRFPService::GetSpoofedModifierStates(
+    const dom::Document* aDoc, const WidgetKeyboardEvent* aKeyboardEvent,
+    const Modifiers aModifier, bool& aOut) {
+  MOZ_ASSERT(aKeyboardEvent);
+
+  // For modifier or control keys, we don't need to hide its modifier states.
+  if (aKeyboardEvent->mKeyNameIndex != KEY_NAME_INDEX_USE_STRING) {
+    return false;
+  }
+
+  // We will spoof the modifer state for Alt, Shift, and AltGraph.
+  // We don't spoof the Control key, because it is often used
+  // for command key combinations in web apps.
+  if ((aModifier & (MODIFIER_ALT | MODIFIER_SHIFT | MODIFIER_ALTGRAPH)) != 0) {
+    SpoofingKeyboardCode keyCodeInfo;
+
+    if (GetSpoofedKeyCodeInfo(aDoc, aKeyboardEvent, keyCodeInfo)) {
+      aOut = ((keyCodeInfo.mModifierStates & aModifier) != 0);
+      return true;
+    }
+  }
+
+  return false;
+}
+
+/* static */
+bool nsRFPService::GetSpoofedCode(const dom::Document* aDoc,
+                                  const WidgetKeyboardEvent* aKeyboardEvent,
+                                  nsAString& aOut) {
+  MOZ_ASSERT(aKeyboardEvent);
+
+  SpoofingKeyboardCode keyCodeInfo;
+
+  if (!GetSpoofedKeyCodeInfo(aDoc, aKeyboardEvent, keyCodeInfo)) {
+    return false;
+  }
+
+  WidgetKeyboardEvent::GetDOMCodeName(keyCodeInfo.mCode, aOut);
+
+  // We need to change the 'Left' with 'Right' if the location indicates
+  // it's a right key.
+  if (aKeyboardEvent->mLocation ==
+          dom::KeyboardEvent_Binding::DOM_KEY_LOCATION_RIGHT &&
+      StringEndsWith(aOut, u"Left"_ns)) {
+    aOut.ReplaceLiteral(aOut.Length() - 4, 4, u"Right");
+  }
+
+  return true;
+}
+
+/* static */
+bool nsRFPService::GetSpoofedKeyCode(const dom::Document* aDoc,
+                                     const WidgetKeyboardEvent* aKeyboardEvent,
+                                     uint32_t& aOut) {
+  MOZ_ASSERT(aKeyboardEvent);
+
+  SpoofingKeyboardCode keyCodeInfo;
+
+  if (GetSpoofedKeyCodeInfo(aDoc, aKeyboardEvent, keyCodeInfo)) {
+    aOut = keyCodeInfo.mKeyCode;
+    return true;
+  }
+
+  return false;
+}
+
+// ============================================================================
+// ============================================================================
+// ============================================================================
+// Randomization Stuff
+nsresult nsRFPService::EnsureSessionKey(bool aIsPrivate) {
+  MOZ_ASSERT(XRE_IsParentProcess());
+
+  MOZ_LOG(gResistFingerprintingLog, LogLevel::Info,
+          ("Ensure the session key for %s browsing session\n",
+           aIsPrivate ? "private" : "normal"));
+
+  if (!StaticPrefs::privacy_resistFingerprinting_randomization_enabled()) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  Maybe<nsID>& sessionKey =
+      aIsPrivate ? mPrivateBrowsingSessionKey : mBrowsingSessionKey;
+
+  // The key has been generated, bail out earlier.
+  if (sessionKey) {
+    MOZ_LOG(
+        gResistFingerprintingLog, LogLevel::Info,
+        ("The %s session key exists: %s\n", aIsPrivate ? "private" : "normal",
+         sessionKey.ref().ToString().get()));
+    return NS_OK;
+  }
+
+  sessionKey.emplace(nsID::GenerateUUID());
+
+  MOZ_LOG(gResistFingerprintingLog, LogLevel::Debug,
+          ("Generated %s session key: %s\n", aIsPrivate ? "private" : "normal",
+           sessionKey.ref().ToString().get()));
+
+  return NS_OK;
+}
+
+void nsRFPService::ClearSessionKey(bool aIsPrivate) {
+  MOZ_ASSERT(XRE_IsParentProcess());
+
+  Maybe<nsID>& sessionKey =
+      aIsPrivate ? mPrivateBrowsingSessionKey : mBrowsingSessionKey;
+
+  sessionKey.reset();
+}
+
+// static
+Maybe<nsTArray<uint8_t>> nsRFPService::GenerateKey(nsIURI* aTopLevelURI,
+                                                   bool aIsPrivate) {
+  MOZ_ASSERT(XRE_IsParentProcess());
+  MOZ_ASSERT(aTopLevelURI);
+
+  MOZ_LOG(gResistFingerprintingLog, LogLevel::Debug,
+          ("Generating %s randomization key for top-level URI: %s\n",
+           aIsPrivate ? "private" : "normal",
+           aTopLevelURI->GetSpecOrDefault().get()));
+
+  RefPtr<nsRFPService> service = GetOrCreate();
+
+  if (NS_FAILED(service->EnsureSessionKey(aIsPrivate))) {
+    return Nothing();
+  }
+
+  // Return nothing if fingerprinting resistance is disabled or fingerprinting
+  // resistance is exempted from the normal windows. Note that we still need to
+  // generate the key for exempted domains because there could be unexempted
+  // sub-documents that need the key.
+  if (!nsContentUtils::ShouldResistFingerprinting(
+          "Coarse Efficiency Check", RFPTarget::CanvasRandomization) ||
+      (!aIsPrivate &&
+       StaticPrefs::privacy_resistFingerprinting_testGranularityMask() &
+           0x02 /* NonPBMExemptMask */)) {
+    return Nothing();
+  }
+
+  const nsID& sessionKey = aIsPrivate
+                               ? service->mPrivateBrowsingSessionKey.ref()
+                               : service->mBrowsingSessionKey.ref();
+
+  auto sessionKeyStr = sessionKey.ToString();
+
+  // Using the OriginAttributes to get the site from the top-level URI. The site
+  // is composed of scheme, host, and port.
+  OriginAttributes attrs;
+  attrs.SetPartitionKey(aTopLevelURI);
+
+  // Generate the key by using the hMAC. The key is based on the session key and
+  // the partitionKey, i.e. top-level site.
+  HMAC hmac;
+
+  nsresult rv = hmac.Begin(
+      SEC_OID_SHA256,
+      Span(reinterpret_cast<const uint8_t*>(sessionKeyStr.get()), NSID_LENGTH));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return Nothing();
+  }
+
+  NS_ConvertUTF16toUTF8 topLevelSite(attrs.mPartitionKey);
+  rv = hmac.Update(reinterpret_cast<const uint8_t*>(topLevelSite.get()),
+                   topLevelSite.Length());
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return Nothing();
+  }
+
+  Maybe<nsTArray<uint8_t>> key;
+  key.emplace();
+
+  rv = hmac.End(key.ref());
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return Nothing();
+  }
+
+  return key;
+}
+
+// static
+nsresult nsRFPService::GenerateCanvasKeyFromImageData(
+    nsICookieJarSettings* aCookieJarSettings, uint8_t* aImageData,
+    uint32_t aSize, nsTArray<uint8_t>& aCanvasKey) {
+  NS_ENSURE_ARG_POINTER(aCookieJarSettings);
+
+  nsTArray<uint8_t> randomKey;
+  nsresult rv =
+      aCookieJarSettings->GetFingerprintingRandomizationKey(randomKey);
+
+  // There is no random key for this cookieJarSettings. This means that the
+  // randomization is disabled. So, we can bail out from here without doing
+  // anything.
+  if (NS_FAILED(rv)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // Generate the key for randomizing the canvas data using hMAC. The key is
+  // based on the random key of the document and the canvas data itself. So,
+  // different canvas would have different keys.
+  HMAC hmac;
+
+  rv = hmac.Begin(SEC_OID_SHA256, Span(randomKey));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = hmac.Update(aImageData, aSize);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = hmac.End(aCanvasKey);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  return NS_OK;
+}
+
+// static
+nsresult nsRFPService::RandomizePixels(nsICookieJarSettings* aCookieJarSettings,
+                                       uint8_t* aData, uint32_t aSize,
+                                       gfx::SurfaceFormat aSurfaceFormat) {
+  NS_ENSURE_ARG_POINTER(aData);
+
+  if (!aCookieJarSettings) {
+    return NS_OK;
+  }
+
+  if (aSize == 0) {
+    return NS_OK;
+  }
+
+  nsTArray<uint8_t> canvasKey;
+  nsresult rv = GenerateCanvasKeyFromImageData(aCookieJarSettings, aData, aSize,
+                                               canvasKey);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // Calculate the number of pixels based on the given data size. One pixel uses
+  // 4 bytes that contains ARGB information.
+  uint32_t pixelCnt = aSize / 4;
+
+  // Generate random values that will decide the RGB channel and the pixel
+  // position that we are going to introduce the noises. The channel and
+  // position are predictable to ensure we have a consistant result with the
+  // same canvas in the same browsing session.
+
+  // Seed and create the first random number generator which will be used to
+  // select RGB channel and the pixel position. The seed is the first half of
+  // the canvas key.
+  non_crypto::XorShift128PlusRNG rng1(
+      *reinterpret_cast<uint64_t*>(canvasKey.Elements()),
+      *reinterpret_cast<uint64_t*>(canvasKey.Elements() + 8));
+
+  // Use the last 8 bits as the number of noises.
+  uint8_t rnd3 = canvasKey.LastElement();
+
+  // Clear the last 8 bits.
+  canvasKey.ReplaceElementAt(canvasKey.Length() - 1, 0);
+
+  // Use the remaining 120 bits to seed and create the second random number
+  // generator. The random number will be used to decided the noise bit that
+  // will be added to the lowest order bit of the channel of the pixel.
+  non_crypto::XorShift128PlusRNG rng2(
+      *reinterpret_cast<uint64_t*>(canvasKey.Elements() + 16),
+      *reinterpret_cast<uint64_t*>(canvasKey.Elements() + 24));
+
+  // Ensure at least 16 random changes may occur.
+  uint8_t numNoises = std::clamp<uint8_t>(rnd3, 15, 255);
+
+  for (uint8_t i = 0; i <= numNoises; i++) {
+    // Choose which RGB channel to add a noise. The pixel data is in either
+    // the BGRA or the ARGB format depending on the endianess. To choose the
+    // color channel we need to add the offset according the endianess.
+    uint32_t channel;
+    if (aSurfaceFormat == gfx::SurfaceFormat::B8G8R8A8) {
+      channel = rng1.next() % 3;
+    } else if (aSurfaceFormat == gfx::SurfaceFormat::A8R8G8B8) {
+      channel = rng1.next() % 3 + 1;
+    } else {
+      return NS_ERROR_INVALID_ARG;
+    }
+
+    uint32_t idx = 4 * (rng1.next() % pixelCnt) + channel;
+    uint8_t bit = rng2.next();
+
+    aData[idx] = aData[idx] ^ (bit & 0x1);
+  }
+
+  return NS_OK;
+}
diff --git a/toolkit/components/resistfingerprinting/nsRFPService.h b/toolkit/components/resistfingerprinting/nsRFPService.h
new file mode 100644
index 0000000000..abb84af116
--- /dev/null
+++ b/toolkit/components/resistfingerprinting/nsRFPService.h
@@ -0,0 +1,349 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * 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/. */
+
+#ifndef __nsRFPService_h__
+#define __nsRFPService_h__
+
+#include <cstdint>
+#include "ErrorList.h"
+#include "PLDHashTable.h"
+#include "mozilla/BasicEvents.h"
+#include "mozilla/gfx/Types.h"
+#include "nsHashtablesFwd.h"
+#include "nsICookieJarSettings.h"
+#include "nsIObserver.h"
+#include "nsISupports.h"
+#include "nsStringFwd.h"
+
+// Defines regarding spoofed values of Navigator object. These spoofed values
+// are returned when 'privacy.resistFingerprinting' is true.
+// We decided to give different spoofed values according to the platform. The
+// reason is that it is easy to detect the real platform. So there is no benefit
+// for hiding the platform: it only brings breakages, like keyboard shortcuts
+// won't work in macOS if we spoof it as a Windows platform.
+#ifdef XP_WIN
+#  define SPOOFED_UA_OS "Windows NT 10.0; Win64; x64"
+#  define SPOOFED_APPVERSION "5.0 (Windows)"
+#  define SPOOFED_OSCPU "Windows NT 10.0; Win64; x64"
+#  define SPOOFED_PLATFORM "Win32"
+#elif defined(XP_MACOSX)
+#  define SPOOFED_UA_OS "Macintosh; Intel Mac OS X 10.15"
+#  define SPOOFED_APPVERSION "5.0 (Macintosh)"
+#  define SPOOFED_OSCPU "Intel Mac OS X 10.15"
+#  define SPOOFED_PLATFORM "MacIntel"
+#elif defined(MOZ_WIDGET_ANDROID)
+#  define SPOOFED_UA_OS "Android 10; Mobile"
+#  define SPOOFED_APPVERSION "5.0 (Android 10)"
+#  define SPOOFED_OSCPU "Linux aarch64"
+#  define SPOOFED_PLATFORM "Linux aarch64"
+#else
+// For Linux and other platforms, like BSDs, SunOS and etc, we will use Linux
+// platform.
+#  define SPOOFED_UA_OS "X11; Linux x86_64"
+#  define SPOOFED_APPVERSION "5.0 (X11)"
+#  define SPOOFED_OSCPU "Linux x86_64"
+#  define SPOOFED_PLATFORM "Linux x86_64"
+#endif
+
+#define SPOOFED_APPNAME "Netscape"
+#define LEGACY_BUILD_ID "20181001000000"
+#define LEGACY_UA_GECKO_TRAIL "20100101"
+
+#define SPOOFED_POINTER_INTERFACE MouseEvent_Binding::MOZ_SOURCE_MOUSE
+
+// For the HTTP User-Agent header, we use a simpler set of spoofed values
+// that do not reveal the specific desktop platform.
+#if defined(MOZ_WIDGET_ANDROID)
+#  define SPOOFED_HTTP_UA_OS "Android 10; Mobile"
+#else
+#  define SPOOFED_HTTP_UA_OS "Windows NT 10.0"
+#endif
+
+struct JSContext;
+
+namespace mozilla {
+class WidgetKeyboardEvent;
+namespace dom {
+class Document;
+}
+
+enum KeyboardLang { EN = 0x01 };
+
+#define RFP_KEYBOARD_LANG_STRING_EN "en"
+
+typedef uint8_t KeyboardLangs;
+
+enum KeyboardRegion { US = 0x01 };
+
+#define RFP_KEYBOARD_REGION_STRING_US "US"
+
+typedef uint8_t KeyboardRegions;
+
+// This struct has the information about how to spoof the keyboardEvent.code,
+// keyboardEvent.keycode and modifier states.
+struct SpoofingKeyboardCode {
+  CodeNameIndex mCode;
+  uint8_t mKeyCode;
+  Modifiers mModifierStates;
+};
+
+struct SpoofingKeyboardInfo {
+  nsString mKey;
+  KeyNameIndex mKeyIdx;
+  SpoofingKeyboardCode mSpoofingCode;
+};
+
+class KeyboardHashKey : public PLDHashEntryHdr {
+ public:
+  typedef const KeyboardHashKey& KeyType;
+  typedef const KeyboardHashKey* KeyTypePointer;
+
+  KeyboardHashKey(const KeyboardLangs aLang, const KeyboardRegions aRegion,
+                  const KeyNameIndexType aKeyIdx, const nsAString& aKey);
+
+  explicit KeyboardHashKey(KeyTypePointer aOther);
+
+  KeyboardHashKey(KeyboardHashKey&& aOther) noexcept;
+
+  ~KeyboardHashKey();
+
+  bool KeyEquals(KeyTypePointer aOther) const;
+
+  static KeyTypePointer KeyToPointer(KeyType aKey);
+
+  static PLDHashNumber HashKey(KeyTypePointer aKey);
+
+  enum { ALLOW_MEMMOVE = true };
+
+  KeyboardLangs mLang;
+  KeyboardRegions mRegion;
+  KeyNameIndexType mKeyIdx;
+  nsString mKey;
+};
+
+// ============================================================================
+
+// Reduce Timer Precision (RTP) Caller Type
+enum class RTPCallerType : uint8_t {
+  Normal = 0,
+  SystemPrincipal = (1 << 0),
+  ResistFingerprinting = (1 << 1),
+  CrossOriginIsolated = (1 << 2)
+};
+
+enum TimerPrecisionType {
+  DangerouslyNone = 1,
+  UnconditionalAKAHighRes = 2,
+  Normal = 3,
+  RFP = 4,
+};
+
+// ============================================================================
+
+// NOLINTNEXTLINE(bugprone-macro-parentheses)
+#define ITEM_VALUE(name, val) name = val,
+
+enum class RFPTarget : uint32_t {
+#include "RFPTargets.inc"
+};
+
+#undef ITEM_VALUE
+
+// ============================================================================
+
+class nsRFPService final : public nsIObserver {
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+
+  static nsRFPService* GetOrCreate();
+
+  static bool IsRFPEnabledFor(RFPTarget aTarget);
+
+  // --------------------------------------------------------------------------
+  static double TimerResolution(RTPCallerType aRTPCallerType);
+
+  enum TimeScale { Seconds = 1, MilliSeconds = 1000, MicroSeconds = 1000000 };
+
+  // The following Reduce methods can be called off main thread.
+  static double ReduceTimePrecisionAsUSecs(double aTime, int64_t aContextMixin,
+                                           RTPCallerType aRTPCallerType);
+  static double ReduceTimePrecisionAsMSecs(double aTime, int64_t aContextMixin,
+                                           RTPCallerType aRTPCallerType);
+  static double ReduceTimePrecisionAsMSecsRFPOnly(double aTime,
+                                                  int64_t aContextMixin,
+                                                  RTPCallerType aRTPCallerType);
+  static double ReduceTimePrecisionAsSecs(double aTime, int64_t aContextMixin,
+                                          RTPCallerType aRTPCallerType);
+  static double ReduceTimePrecisionAsSecsRFPOnly(double aTime,
+                                                 int64_t aContextMixin,
+                                                 RTPCallerType aRTPCallerType);
+
+  // Used by the JS Engine, as it doesn't know about the TimerPrecisionType enum
+  static double ReduceTimePrecisionAsUSecsWrapper(
+      double aTime, bool aShouldResistFingerprinting, JSContext* aCx);
+
+  // Public only for testing purposes
+  static double ReduceTimePrecisionImpl(double aTime, TimeScale aTimeScale,
+                                        double aResolutionUSec,
+                                        int64_t aContextMixin,
+                                        TimerPrecisionType aType);
+  static nsresult RandomMidpoint(long long aClampedTimeUSec,
+                                 long long aResolutionUSec,
+                                 int64_t aContextMixin, long long* aMidpointOut,
+                                 uint8_t* aSecretSeed = nullptr);
+
+  // --------------------------------------------------------------------------
+
+  // This method calculates the video resolution (i.e. height x width) based
+  // on the video quality (480p, 720p, etc).
+  static uint32_t CalculateTargetVideoResolution(uint32_t aVideoQuality);
+
+  // Methods for getting spoofed media statistics and the return value will
+  // depend on the video resolution.
+  static uint32_t GetSpoofedTotalFrames(double aTime);
+  static uint32_t GetSpoofedDroppedFrames(double aTime, uint32_t aWidth,
+                                          uint32_t aHeight);
+  static uint32_t GetSpoofedPresentedFrames(double aTime, uint32_t aWidth,
+                                            uint32_t aHeight);
+
+  // --------------------------------------------------------------------------
+
+  // This method generates the spoofed value of User Agent.
+  static void GetSpoofedUserAgent(nsACString& userAgent, bool isForHTTPHeader);
+
+  // --------------------------------------------------------------------------
+
+  /**
+   * This method for getting spoofed modifier states for the given keyboard
+   * event.
+   *
+   * @param aDoc           [in]  the owner's document for getting content
+   *                             language.
+   * @param aKeyboardEvent [in]  the keyboard event that needs to be spoofed.
+   * @param aModifier      [in]  the modifier that needs to be spoofed.
+   * @param aOut           [out] the spoofed state for the given modifier.
+   * @return               true if there is a spoofed state for the modifier.
+   */
+  static bool GetSpoofedModifierStates(
+      const mozilla::dom::Document* aDoc,
+      const WidgetKeyboardEvent* aKeyboardEvent, const Modifiers aModifier,
+      bool& aOut);
+
+  /**
+   * This method for getting spoofed code for the given keyboard event.
+   *
+   * @param aDoc           [in]  the owner's document for getting content
+   *                             language.
+   * @param aKeyboardEvent [in]  the keyboard event that needs to be spoofed.
+   * @param aOut           [out] the spoofed code.
+   * @return               true if there is a spoofed code in the fake keyboard
+   *                       layout.
+   */
+  static bool GetSpoofedCode(const dom::Document* aDoc,
+                             const WidgetKeyboardEvent* aKeyboardEvent,
+                             nsAString& aOut);
+
+  /**
+   * This method for getting spoofed keyCode for the given keyboard event.
+   *
+   * @param aDoc           [in]  the owner's document for getting content
+   *                             language.
+   * @param aKeyboardEvent [in]  the keyboard event that needs to be spoofed.
+   * @param aOut           [out] the spoofed keyCode.
+   * @return               true if there is a spoofed keyCode in the fake
+   *                       keyboard layout.
+   */
+  static bool GetSpoofedKeyCode(const mozilla::dom::Document* aDoc,
+                                const WidgetKeyboardEvent* aKeyboardEvent,
+                                uint32_t& aOut);
+
+  // --------------------------------------------------------------------------
+
+  // The method to generate the key for randomization. It can return nothing if
+  // the session key is not available due to the randomization is disabled.
+  static Maybe<nsTArray<uint8_t>> GenerateKey(nsIURI* aTopLevelURI,
+                                              bool aIsPrivate);
+
+  // The method to add random noises to the image data based on the random key
+  // of the given cookieJarSettings.
+  static nsresult RandomizePixels(nsICookieJarSettings* aCookieJarSettings,
+                                  uint8_t* aData, uint32_t aSize,
+                                  mozilla::gfx::SurfaceFormat aSurfaceFormat);
+
+  // --------------------------------------------------------------------------
+
+ private:
+  nsresult Init();
+
+  nsRFPService() = default;
+
+  ~nsRFPService() = default;
+
+  nsCString mInitialTZValue;
+
+  void UpdateRFPPref();
+  void UpdateFPPOverrideList();
+  void StartShutdown();
+
+  void PrefChanged(const char* aPref);
+  static void PrefChanged(const char* aPref, void* aSelf);
+
+  static Maybe<RFPTarget> TextToRFPTarget(const nsAString& aText);
+
+  // --------------------------------------------------------------------------
+
+  static void MaybeCreateSpoofingKeyCodes(const KeyboardLangs aLang,
+                                          const KeyboardRegions aRegion);
+  static void MaybeCreateSpoofingKeyCodesForEnUS();
+
+  static void GetKeyboardLangAndRegion(const nsAString& aLanguage,
+                                       KeyboardLangs& aLocale,
+                                       KeyboardRegions& aRegion);
+  static bool GetSpoofedKeyCodeInfo(const mozilla::dom::Document* aDoc,
+                                    const WidgetKeyboardEvent* aKeyboardEvent,
+                                    SpoofingKeyboardCode& aOut);
+
+  static nsTHashMap<KeyboardHashKey, const SpoofingKeyboardCode*>*
+      sSpoofingKeyboardCodes;
+
+  // --------------------------------------------------------------------------
+
+  static TimerPrecisionType GetTimerPrecisionType(RTPCallerType aRTPCallerType);
+
+  static TimerPrecisionType GetTimerPrecisionTypeRFPOnly(
+      RTPCallerType aRTPCallerType);
+
+  static void TypeToText(TimerPrecisionType aType, nsACString& aText);
+
+  // --------------------------------------------------------------------------
+
+  // A helper function to generate canvas key from the given image data and
+  // randomization key.
+  static nsresult GenerateCanvasKeyFromImageData(
+      nsICookieJarSettings* aCookieJarSettings, uint8_t* aImageData,
+      uint32_t aSize, nsTArray<uint8_t>& aCanvasKey);
+
+  // Generate the session key if it hasn't been generated.
+  nsresult EnsureSessionKey(bool aIsPrivate);
+  void ClearSessionKey(bool aIsPrivate);
+
+  // The keys that represent the browsing session. The lifetime of the key ties
+  // to the browsing session. For normal windows, the key is generated when
+  // loading the first http channel after the browser startup and persists until
+  // the browser shuts down. For private windows, the key is generated when
+  // opening a http channel on a private window and reset after all private
+  // windows close, i.e. private browsing session ends.
+  //
+  // The key will be used to generate the randomization noise used to fiddle the
+  // browser fingerprints. Note that this key lives and can only be accessed in
+  // the parent process.
+  Maybe<nsID> mBrowsingSessionKey;
+  Maybe<nsID> mPrivateBrowsingSessionKey;
+};
+
+}  // namespace mozilla
+
+#endif /* __nsRFPService_h__ */
diff --git a/toolkit/components/resistfingerprinting/tests/browser/browser.ini b/toolkit/components/resistfingerprinting/tests/browser/browser.ini
new file mode 100644
index 0000000000..3a3aa2ccc6
--- /dev/null
+++ b/toolkit/components/resistfingerprinting/tests/browser/browser.ini
@@ -0,0 +1,10 @@
+[DEFAULT]
+support-files =
+  empty.html
+  head.js
+  testPage.html
+  worker.js
+
+[browser_canvas_randomization.js]
+[browser_canvas_randomization_worker.js]
+[browser_fingerprinting_randomization_key.js]
diff --git a/toolkit/components/resistfingerprinting/tests/browser/browser_canvas_randomization.js b/toolkit/components/resistfingerprinting/tests/browser/browser_canvas_randomization.js
new file mode 100644
index 0000000000..0935beecba
--- /dev/null
+++ b/toolkit/components/resistfingerprinting/tests/browser/browser_canvas_randomization.js
@@ -0,0 +1,589 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * 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/. */
+
+/**
+ * Bug 1816189 - Testing canvas randomization on canvas data extraction.
+ *
+ * In the test, we create canvas elements and offscreen canvas and test if
+ * the extracted canvas data is altered because of the canvas randomization.
+ */
+
+const emptyPage =
+  getRootDirectory(gTestPath).replace(
+    "chrome://mochitests/content",
+    "https://example.com"
+  ) + "empty.html";
+
+var TEST_CASES = [
+  {
+    name: "CanvasRenderingContext2D.getImageData().",
+    extractCanvasData(browser) {
+      return SpecialPowers.spawn(browser, [], _ => {
+        const canvas = content.document.createElement("canvas");
+        canvas.width = 100;
+        canvas.height = 100;
+
+        const context = canvas.getContext("2d");
+
+        // Draw a red rectangle
+        context.fillStyle = "red";
+        context.fillRect(0, 0, 100, 100);
+
+        // Add the canvas element to the document
+        content.document.body.appendChild(canvas);
+
+        const imageData = context.getImageData(0, 0, 100, 100);
+
+        // Access the data again.
+        const imageDataSecond = context.getImageData(0, 0, 100, 100);
+
+        return [imageData.data, imageDataSecond.data];
+      });
+    },
+    isDataRandomized(data1, data2, isCompareOriginal) {
+      let diffCnt = compareUint8Arrays(data1, data2);
+      info(`There are ${diffCnt} bits are different.`);
+
+      // The Canvas randomization adds at most 512 bits noise to the image data.
+      // We compare the image data arrays to see if they are different and the
+      // difference is within the range.
+
+      // If we are compare two randomized arrays, the difference can be doubled.
+      let expected = isCompareOriginal
+        ? NUM_RANDOMIZED_CANVAS_BITS
+        : NUM_RANDOMIZED_CANVAS_BITS * 2;
+
+      // The number of difference bits should never bigger than the expected
+      // number. It could be zero if the randomization is disabled.
+      ok(diffCnt <= expected, "The number of noise bits is expected.");
+
+      return diffCnt <= expected && diffCnt > 0;
+    },
+  },
+  {
+    name: "HTMLCanvasElement.toDataURL() with a 2d context",
+    extractCanvasData(browser) {
+      return SpecialPowers.spawn(browser, [], _ => {
+        const canvas = content.document.createElement("canvas");
+        canvas.width = 100;
+        canvas.height = 100;
+
+        const context = canvas.getContext("2d");
+
+        // Draw a red rectangle
+        context.fillStyle = "red";
+        context.fillRect(0, 0, 100, 100);
+
+        // Add the canvas element to the document
+        content.document.body.appendChild(canvas);
+
+        const dataURL = canvas.toDataURL();
+
+        // Access the data again.
+        const dataURLSecond = canvas.toDataURL();
+
+        return [dataURL, dataURLSecond];
+      });
+    },
+    isDataRandomized(data1, data2) {
+      return data1 !== data2;
+    },
+  },
+  {
+    name: "HTMLCanvasElement.toDataURL() with a webgl context",
+    extractCanvasData(browser) {
+      return SpecialPowers.spawn(browser, [], _ => {
+        const canvas = content.document.createElement("canvas");
+
+        const context = canvas.getContext("webgl");
+
+        // Draw a blue rectangle
+        context.enable(context.SCISSOR_TEST);
+        context.scissor(0, 150, 150, 150);
+        context.clearColor(1, 0, 0, 1);
+        context.clear(context.COLOR_BUFFER_BIT);
+        context.scissor(150, 150, 300, 150);
+        context.clearColor(0, 1, 0, 1);
+        context.clear(context.COLOR_BUFFER_BIT);
+        context.scissor(0, 0, 150, 150);
+        context.clearColor(0, 0, 1, 1);
+        context.clear(context.COLOR_BUFFER_BIT);
+
+        // Add the canvas element to the document
+        content.document.body.appendChild(canvas);
+
+        const dataURL = canvas.toDataURL();
+
+        // Access the data again.
+        const dataURLSecond = canvas.toDataURL();
+
+        return [dataURL, dataURLSecond];
+      });
+    },
+    isDataRandomized(data1, data2) {
+      return data1 !== data2;
+    },
+  },
+  {
+    name: "HTMLCanvasElement.toDataURL() with a bitmaprenderer context",
+    extractCanvasData(browser) {
+      return SpecialPowers.spawn(browser, [], async _ => {
+        const canvas = content.document.createElement("canvas");
+        canvas.width = 100;
+        canvas.height = 100;
+
+        const context = canvas.getContext("2d");
+
+        // Draw a red rectangle
+        context.fillStyle = "red";
+        context.fillRect(0, 0, 100, 100);
+
+        // Add the canvas element to the document
+        content.document.body.appendChild(canvas);
+
+        const bitmapCanvas = content.document.createElement("canvas");
+        bitmapCanvas.width = 100;
+        bitmapCanvas.heigh = 100;
+        content.document.body.appendChild(bitmapCanvas);
+
+        let bitmap = await content.createImageBitmap(canvas);
+        const bitmapContext = bitmapCanvas.getContext("bitmaprenderer");
+        bitmapContext.transferFromImageBitmap(bitmap);
+
+        const dataURL = bitmapCanvas.toDataURL();
+
+        // Access the data again.
+        const dataURLSecond = bitmapCanvas.toDataURL();
+
+        return [dataURL, dataURLSecond];
+      });
+    },
+    isDataRandomized(data1, data2) {
+      return data1 !== data2;
+    },
+  },
+  {
+    name: "HTMLCanvasElement.toBlob() with a 2d context",
+    extractCanvasData(browser) {
+      return SpecialPowers.spawn(browser, [], async _ => {
+        const canvas = content.document.createElement("canvas");
+        canvas.width = 100;
+        canvas.height = 100;
+
+        const context = canvas.getContext("2d");
+
+        // Draw a red rectangle
+        context.fillStyle = "red";
+        context.fillRect(0, 0, 100, 100);
+
+        // Add the canvas element to the document
+        content.document.body.appendChild(canvas);
+
+        let data = await new content.Promise(resolve => {
+          canvas.toBlob(blob => {
+            let fileReader = new content.FileReader();
+            fileReader.onload = () => {
+              resolve(fileReader.result);
+            };
+            fileReader.readAsArrayBuffer(blob);
+          });
+        });
+
+        // Access the data again.
+        let dataSecond = await new content.Promise(resolve => {
+          canvas.toBlob(blob => {
+            let fileReader = new content.FileReader();
+            fileReader.onload = () => {
+              resolve(fileReader.result);
+            };
+            fileReader.readAsArrayBuffer(blob);
+          });
+        });
+
+        return [data, dataSecond];
+      });
+    },
+    isDataRandomized(data1, data2) {
+      return compareArrayBuffer(data1, data2);
+    },
+  },
+  {
+    name: "HTMLCanvasElement.toBlob() with a webgl context",
+    extractCanvasData(browser) {
+      return SpecialPowers.spawn(browser, [], async _ => {
+        const canvas = content.document.createElement("canvas");
+
+        const context = canvas.getContext("webgl");
+
+        // Draw a blue rectangle
+        context.enable(context.SCISSOR_TEST);
+        context.scissor(0, 150, 150, 150);
+        context.clearColor(1, 0, 0, 1);
+        context.clear(context.COLOR_BUFFER_BIT);
+        context.scissor(150, 150, 300, 150);
+        context.clearColor(0, 1, 0, 1);
+        context.clear(context.COLOR_BUFFER_BIT);
+        context.scissor(0, 0, 150, 150);
+        context.clearColor(0, 0, 1, 1);
+        context.clear(context.COLOR_BUFFER_BIT);
+
+        // Add the canvas element to the document
+        content.document.body.appendChild(canvas);
+
+        let data = await new content.Promise(resolve => {
+          canvas.toBlob(blob => {
+            let fileReader = new content.FileReader();
+            fileReader.onload = () => {
+              resolve(fileReader.result);
+            };
+            fileReader.readAsArrayBuffer(blob);
+          });
+        });
+
+        // We don't get the consistent blob data on second access with webgl
+        // context regardless of the canvas randomization. So, we report the
+        // same data here to not fail the test. Ideally, we should look into
+        // why this happens, but it's not caused by canvas randomization.
+
+        return [data, data];
+      });
+    },
+    isDataRandomized(data1, data2) {
+      return compareArrayBuffer(data1, data2);
+    },
+  },
+  {
+    name: "HTMLCanvasElement.toBlob() with a bitmaprenderer context",
+    extractCanvasData(browser) {
+      return SpecialPowers.spawn(browser, [], async _ => {
+        const canvas = content.document.createElement("canvas");
+        canvas.width = 100;
+        canvas.height = 100;
+
+        const context = canvas.getContext("2d");
+
+        // Draw a red rectangle
+        context.fillStyle = "red";
+        context.fillRect(0, 0, 100, 100);
+
+        // Add the canvas element to the document
+        content.document.body.appendChild(canvas);
+
+        const bitmapCanvas = content.document.createElement("canvas");
+        bitmapCanvas.width = 100;
+        bitmapCanvas.heigh = 100;
+        content.document.body.appendChild(bitmapCanvas);
+
+        let bitmap = await content.createImageBitmap(canvas);
+        const bitmapContext = bitmapCanvas.getContext("bitmaprenderer");
+        bitmapContext.transferFromImageBitmap(bitmap);
+
+        let data = await new content.Promise(resolve => {
+          bitmapCanvas.toBlob(blob => {
+            let fileReader = new content.FileReader();
+            fileReader.onload = () => {
+              resolve(fileReader.result);
+            };
+            fileReader.readAsArrayBuffer(blob);
+          });
+        });
+
+        // Access the data again.
+        let dataSecond = await new content.Promise(resolve => {
+          bitmapCanvas.toBlob(blob => {
+            let fileReader = new content.FileReader();
+            fileReader.onload = () => {
+              resolve(fileReader.result);
+            };
+            fileReader.readAsArrayBuffer(blob);
+          });
+        });
+
+        return [data, dataSecond];
+      });
+    },
+    isDataRandomized(data1, data2) {
+      return compareArrayBuffer(data1, data2);
+    },
+  },
+  {
+    name: "OffscreenCanvas.convertToBlob() with a 2d context",
+    extractCanvasData(browser) {
+      return SpecialPowers.spawn(browser, [], async _ => {
+        let offscreenCanvas = new content.OffscreenCanvas(100, 100);
+
+        const context = offscreenCanvas.getContext("2d");
+
+        // Draw a red rectangle
+        context.fillStyle = "red";
+        context.fillRect(0, 0, 100, 100);
+
+        let blob = await offscreenCanvas.convertToBlob();
+
+        let data = await new content.Promise(resolve => {
+          let fileReader = new content.FileReader();
+          fileReader.onload = () => {
+            resolve(fileReader.result);
+          };
+          fileReader.readAsArrayBuffer(blob);
+        });
+
+        // Access the data again.
+        let blobSecond = await offscreenCanvas.convertToBlob();
+
+        let dataSecond = await new content.Promise(resolve => {
+          let fileReader = new content.FileReader();
+          fileReader.onload = () => {
+            resolve(fileReader.result);
+          };
+          fileReader.readAsArrayBuffer(blobSecond);
+        });
+
+        return [data, dataSecond];
+      });
+    },
+    isDataRandomized(data1, data2) {
+      return compareArrayBuffer(data1, data2);
+    },
+  },
+  {
+    name: "OffscreenCanvas.convertToBlob() with a webgl context",
+    extractCanvasData(browser) {
+      return SpecialPowers.spawn(browser, [], async _ => {
+        let offscreenCanvas = new content.OffscreenCanvas(100, 100);
+
+        const context = offscreenCanvas.getContext("webgl");
+
+        // Draw a blue rectangle
+        context.enable(context.SCISSOR_TEST);
+        context.scissor(0, 150, 150, 150);
+        context.clearColor(1, 0, 0, 1);
+        context.clear(context.COLOR_BUFFER_BIT);
+        context.scissor(150, 150, 300, 150);
+        context.clearColor(0, 1, 0, 1);
+        context.clear(context.COLOR_BUFFER_BIT);
+        context.scissor(0, 0, 150, 150);
+        context.clearColor(0, 0, 1, 1);
+        context.clear(context.COLOR_BUFFER_BIT);
+
+        let blob = await offscreenCanvas.convertToBlob();
+
+        let data = await new content.Promise(resolve => {
+          let fileReader = new content.FileReader();
+          fileReader.onload = () => {
+            resolve(fileReader.result);
+          };
+          fileReader.readAsArrayBuffer(blob);
+        });
+
+        // Access the data again.
+        let blobSecond = await offscreenCanvas.convertToBlob();
+
+        let dataSecond = await new content.Promise(resolve => {
+          let fileReader = new content.FileReader();
+          fileReader.onload = () => {
+            resolve(fileReader.result);
+          };
+          fileReader.readAsArrayBuffer(blobSecond);
+        });
+
+        return [data, dataSecond];
+      });
+    },
+    isDataRandomized(data1, data2) {
+      return compareArrayBuffer(data1, data2);
+    },
+  },
+  {
+    name: "OffscreenCanvas.convertToBlob() with a bitmaprenderer context",
+    extractCanvasData(browser) {
+      return SpecialPowers.spawn(browser, [], async _ => {
+        let offscreenCanvas = new content.OffscreenCanvas(100, 100);
+
+        const context = offscreenCanvas.getContext("2d");
+
+        // Draw a red rectangle
+        context.fillStyle = "red";
+        context.fillRect(0, 0, 100, 100);
+
+        const bitmapCanvas = new content.OffscreenCanvas(100, 100);
+
+        let bitmap = await content.createImageBitmap(offscreenCanvas);
+        const bitmapContext = bitmapCanvas.getContext("bitmaprenderer");
+        bitmapContext.transferFromImageBitmap(bitmap);
+
+        let blob = await bitmapCanvas.convertToBlob();
+
+        let data = await new content.Promise(resolve => {
+          let fileReader = new content.FileReader();
+          fileReader.onload = () => {
+            resolve(fileReader.result);
+          };
+          fileReader.readAsArrayBuffer(blob);
+        });
+
+        // Access the data again.
+        let blobSecond = await bitmapCanvas.convertToBlob();
+
+        let dataSecond = await new content.Promise(resolve => {
+          let fileReader = new content.FileReader();
+          fileReader.onload = () => {
+            resolve(fileReader.result);
+          };
+          fileReader.readAsArrayBuffer(blobSecond);
+        });
+
+        return [data, dataSecond];
+      });
+    },
+    isDataRandomized(data1, data2) {
+      return compareArrayBuffer(data1, data2);
+    },
+  },
+  {
+    name: "CanvasRenderingContext2D.getImageData() with a offscreen canvas",
+    extractCanvasData(browser) {
+      return SpecialPowers.spawn(browser, [], async _ => {
+        let offscreenCanvas = new content.OffscreenCanvas(100, 100);
+
+        const context = offscreenCanvas.getContext("2d");
+
+        // Draw a red rectangle
+        context.fillStyle = "red";
+        context.fillRect(0, 0, 100, 100);
+
+        const imageData = context.getImageData(0, 0, 100, 100);
+
+        // Access the data again.
+        const imageDataSecond = context.getImageData(0, 0, 100, 100);
+
+        return [imageData.data, imageDataSecond.data];
+      });
+    },
+    isDataRandomized(data1, data2, isCompareOriginal) {
+      let diffCnt = compareUint8Arrays(data1, data2);
+      info(`There are ${diffCnt} bits are different.`);
+
+      // The Canvas randomization adds at most 512 bits noise to the image data.
+      // We compare the image data arrays to see if they are different and the
+      // difference is within the range.
+
+      // If we are compare two randomized arrays, the difference can be doubled.
+      let expected = isCompareOriginal
+        ? NUM_RANDOMIZED_CANVAS_BITS
+        : NUM_RANDOMIZED_CANVAS_BITS * 2;
+
+      // The number of difference bits should never bigger than the expected
+      // number. It could be zero if the randomization is disabled.
+      ok(diffCnt <= expected, "The number of noise bits is expected.");
+
+      return diffCnt <= expected && diffCnt > 0;
+    },
+  },
+];
+
+async function runTest(enabled) {
+  // Enable/Disable CanvasRandomization by the RFP target overrides.
+  let RFPOverrides = enabled ? "+CanvasRandomization" : "-CanvasRandomization";
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["privacy.resistFingerprinting.randomization.enabled", true],
+      ["privacy.fingerprintingProtection", true],
+      ["privacy.fingerprintingProtection.pbmode", true],
+      ["privacy.fingerprintingProtection.overrides", RFPOverrides],
+      ["privacy.resistFingerprinting", false],
+    ],
+  });
+
+  // Open a private window.
+  let privateWindow = await BrowserTestUtils.openNewBrowserWindow({
+    private: true,
+  });
+
+  // Open tabs in the normal and private window.
+  const tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, emptyPage);
+
+  const privateTab = await BrowserTestUtils.openNewForegroundTab(
+    privateWindow.gBrowser,
+    emptyPage
+  );
+
+  for (let test of TEST_CASES) {
+    info(`Testing ${test.name}`);
+    let data = await test.extractCanvasData(tab.linkedBrowser);
+    let result = test.isDataRandomized(data[0], test.originalData);
+
+    is(
+      result,
+      enabled,
+      `The image data is ${enabled ? "randomized" : "the same"}.`
+    );
+
+    ok(
+      !test.isDataRandomized(data[0], data[1]),
+      "The data of first and second access should be the same."
+    );
+
+    let privateData = await test.extractCanvasData(privateTab.linkedBrowser);
+
+    // Check if we add noise to canvas data in private windows.
+    result = test.isDataRandomized(privateData[0], test.originalData, true);
+    is(
+      result,
+      enabled,
+      `The private image data is ${enabled ? "randomized" : "the same"}.`
+    );
+
+    ok(
+      !test.isDataRandomized(privateData[0], privateData[1]),
+      "The data of first and second access should be the same for private windows."
+    );
+
+    // Make sure the noises are different between normal window and private
+    // windows.
+    result = test.isDataRandomized(privateData[0], data[0]);
+    is(
+      result,
+      enabled,
+      `The image data between the normal window and the private window are ${
+        enabled ? "different" : "the same"
+      }.`
+    );
+  }
+
+  BrowserTestUtils.removeTab(tab);
+  BrowserTestUtils.removeTab(privateTab);
+  await BrowserTestUtils.closeWindow(privateWindow);
+}
+
+add_setup(async function () {
+  // Disable the fingerprinting randomization.
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["privacy.resistFingerprinting.randomization.enabled", false],
+      ["privacy.fingerprintingProtection", false],
+      ["privacy.fingerprintingProtection.pbmode", false],
+      ["privacy.resistFingerprinting", false],
+    ],
+  });
+
+  // Open a tab for extracting the canvas data.
+  const tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, emptyPage);
+
+  // Extract the original canvas data without random noise.
+  for (let test of TEST_CASES) {
+    let data = await test.extractCanvasData(tab.linkedBrowser);
+    test.originalData = data[0];
+  }
+
+  BrowserTestUtils.removeTab(tab);
+});
+
+add_task(async function run_tests_with_randomization_enabled() {
+  await runTest(true);
+});
+
+add_task(async function run_tests_with_randomization_disabled() {
+  await runTest(false);
+});
diff --git a/toolkit/components/resistfingerprinting/tests/browser/browser_canvas_randomization_worker.js b/toolkit/components/resistfingerprinting/tests/browser/browser_canvas_randomization_worker.js
new file mode 100644
index 0000000000..2f27925c71
--- /dev/null
+++ b/toolkit/components/resistfingerprinting/tests/browser/browser_canvas_randomization_worker.js
@@ -0,0 +1,323 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * 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/. */
+
+const emptyPage =
+  getRootDirectory(gTestPath).replace(
+    "chrome://mochitests/content",
+    "https://example.com"
+  ) + "empty.html";
+
+/**
+ * Bug 1816189 - Testing canvas randomization on canvas data extraction in
+ * workers.
+ *
+ * In the test, we create offscreen canvas in workers and test if the extracted
+ * canvas data is altered because of the canvas randomization.
+ */
+
+/**
+ *
+ * Spawns a worker in the given browser and sends a callback function to it.
+ * The result of the callback function is returned as a Promise.
+ *
+ * @param {object} browser - The browser context to spawn the worker in.
+ * @param {Function} fn - The callback function to send to the worker.
+ * @returns {Promise} A Promise that resolves to the result of the callback function.
+ */
+function runFunctionInWorker(browser, fn) {
+  return SpecialPowers.spawn(browser, [fn.toString()], async callback => {
+    // Create a worker.
+    let worker = new content.Worker("worker.js");
+
+    // Send the callback to the worker.
+    return new content.Promise(resolve => {
+      worker.onmessage = e => {
+        resolve(e.data.result);
+      };
+
+      worker.postMessage({
+        callback,
+      });
+    });
+  });
+}
+
+var TEST_CASES = [
+  {
+    name: "CanvasRenderingContext2D.getImageData() with a offscreen canvas",
+    extractCanvasData: async _ => {
+      let offscreenCanvas = new OffscreenCanvas(100, 100);
+
+      const context = offscreenCanvas.getContext("2d");
+
+      // Draw a red rectangle
+      context.fillStyle = "red";
+      context.fillRect(0, 0, 100, 100);
+
+      const imageData = context.getImageData(0, 0, 100, 100);
+
+      const imageDataSecond = context.getImageData(0, 0, 100, 100);
+
+      return [imageData.data, imageDataSecond.data];
+    },
+    isDataRandomized(data1, data2, isCompareOriginal) {
+      let diffCnt = compareUint8Arrays(data1, data2);
+      info(`There are ${diffCnt} bits are different.`);
+
+      // The Canvas randomization adds at most 512 bits noise to the image data.
+      // We compare the image data arrays to see if they are different and the
+      // difference is within the range.
+
+      // If we are compare two randomized arrays, the difference can be doubled.
+      let expected = isCompareOriginal
+        ? NUM_RANDOMIZED_CANVAS_BITS
+        : NUM_RANDOMIZED_CANVAS_BITS * 2;
+
+      // The number of difference bits should never bigger than the expected
+      // number. It could be zero if the randomization is disabled.
+      ok(diffCnt <= expected, "The number of noise bits is expected.");
+
+      return diffCnt <= expected && diffCnt > 0;
+    },
+  },
+  {
+    name: "OffscreenCanvas.convertToBlob() with a 2d context",
+    extractCanvasData: async _ => {
+      let offscreenCanvas = new OffscreenCanvas(100, 100);
+
+      const context = offscreenCanvas.getContext("2d");
+
+      // Draw a red rectangle
+      context.fillStyle = "red";
+      context.fillRect(0, 0, 100, 100);
+
+      let blob = await offscreenCanvas.convertToBlob();
+
+      let data = await new Promise(resolve => {
+        let fileReader = new FileReader();
+        fileReader.onload = () => {
+          resolve(fileReader.result);
+        };
+        fileReader.readAsArrayBuffer(blob);
+      });
+
+      let blobSecond = await offscreenCanvas.convertToBlob();
+
+      let dataSecond = await new Promise(resolve => {
+        let fileReader = new FileReader();
+        fileReader.onload = () => {
+          resolve(fileReader.result);
+        };
+        fileReader.readAsArrayBuffer(blobSecond);
+      });
+
+      return [data, dataSecond];
+    },
+    isDataRandomized(data1, data2) {
+      return compareArrayBuffer(data1, data2);
+    },
+  },
+  {
+    name: "OffscreenCanvas.convertToBlob() with a webgl context",
+    extractCanvasData: async _ => {
+      let offscreenCanvas = new OffscreenCanvas(100, 100);
+
+      const context = offscreenCanvas.getContext("webgl");
+
+      // Draw a blue rectangle
+      context.enable(context.SCISSOR_TEST);
+      context.scissor(0, 150, 150, 150);
+      context.clearColor(1, 0, 0, 1);
+      context.clear(context.COLOR_BUFFER_BIT);
+      context.scissor(150, 150, 300, 150);
+      context.clearColor(0, 1, 0, 1);
+      context.clear(context.COLOR_BUFFER_BIT);
+      context.scissor(0, 0, 150, 150);
+      context.clearColor(0, 0, 1, 1);
+      context.clear(context.COLOR_BUFFER_BIT);
+
+      let blob = await offscreenCanvas.convertToBlob();
+
+      let data = await new Promise(resolve => {
+        let fileReader = new FileReader();
+        fileReader.onload = () => {
+          resolve(fileReader.result);
+        };
+        fileReader.readAsArrayBuffer(blob);
+      });
+
+      let blobSecond = await offscreenCanvas.convertToBlob();
+
+      let dataSecond = await new Promise(resolve => {
+        let fileReader = new FileReader();
+        fileReader.onload = () => {
+          resolve(fileReader.result);
+        };
+        fileReader.readAsArrayBuffer(blobSecond);
+      });
+
+      return [data, dataSecond];
+    },
+    isDataRandomized(data1, data2) {
+      return compareArrayBuffer(data1, data2);
+    },
+  },
+  {
+    name: "OffscreenCanvas.convertToBlob() with a bitmaprenderer context",
+    extractCanvasData: async _ => {
+      let offscreenCanvas = new OffscreenCanvas(100, 100);
+
+      const context = offscreenCanvas.getContext("2d");
+
+      // Draw a red rectangle
+      context.fillStyle = "red";
+      context.fillRect(0, 0, 100, 100);
+
+      const bitmapCanvas = new OffscreenCanvas(100, 100);
+
+      let bitmap = await createImageBitmap(offscreenCanvas);
+      const bitmapContext = bitmapCanvas.getContext("bitmaprenderer");
+      bitmapContext.transferFromImageBitmap(bitmap);
+
+      let blob = await bitmapCanvas.convertToBlob();
+
+      let data = await new Promise(resolve => {
+        let fileReader = new FileReader();
+        fileReader.onload = () => {
+          resolve(fileReader.result);
+        };
+        fileReader.readAsArrayBuffer(blob);
+      });
+
+      let blobSecond = await bitmapCanvas.convertToBlob();
+
+      let dataSecond = await new Promise(resolve => {
+        let fileReader = new FileReader();
+        fileReader.onload = () => {
+          resolve(fileReader.result);
+        };
+        fileReader.readAsArrayBuffer(blobSecond);
+      });
+
+      return [data, dataSecond];
+    },
+    isDataRandomized(data1, data2) {
+      return compareArrayBuffer(data1, data2);
+    },
+  },
+];
+
+async function runTest(enabled) {
+  // Enable/Disable CanvasRandomization by the RFP target overrides.
+  let RFPOverrides = enabled ? "+CanvasRandomization" : "-CanvasRandomization";
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["privacy.resistFingerprinting.randomization.enabled", true],
+      ["privacy.fingerprintingProtection", true],
+      ["privacy.fingerprintingProtection.pbmode", true],
+      ["privacy.fingerprintingProtection.overrides", RFPOverrides],
+      ["privacy.resistFingerprinting", false],
+    ],
+  });
+
+  // Open a private window.
+  let privateWindow = await BrowserTestUtils.openNewBrowserWindow({
+    private: true,
+  });
+
+  // Open tabs in the normal and private window.
+  const tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, emptyPage);
+
+  const privateTab = await BrowserTestUtils.openNewForegroundTab(
+    privateWindow.gBrowser,
+    emptyPage
+  );
+
+  for (let test of TEST_CASES) {
+    info(`Testing ${test.name} in the worker`);
+    let data = await await runFunctionInWorker(
+      tab.linkedBrowser,
+      test.extractCanvasData
+    );
+
+    let result = test.isDataRandomized(data[0], test.originalData);
+    is(
+      result,
+      enabled,
+      `The image data is ${enabled ? "randomized" : "the same"}.`
+    );
+
+    ok(
+      !test.isDataRandomized(data[0], data[1]),
+      "The data of first and second access should be the same."
+    );
+
+    let privateData = await await runFunctionInWorker(
+      privateTab.linkedBrowser,
+      test.extractCanvasData
+    );
+
+    // Check if we add noise to canvas data in private windows.
+    result = test.isDataRandomized(privateData[0], test.originalData, true);
+    is(
+      result,
+      enabled,
+      `The private image data is ${enabled ? "randomized" : "the same"}.`
+    );
+
+    ok(
+      !test.isDataRandomized(privateData[0], privateData[1]),
+      "The data of first and second access should be the same."
+    );
+
+    // Make sure the noises are different between normal window and private
+    // windows.
+    result = test.isDataRandomized(privateData[0], data[0]);
+    is(
+      result,
+      enabled,
+      `The image data between the normal window and the private window are ${
+        enabled ? "different" : "the same"
+      }.`
+    );
+  }
+
+  BrowserTestUtils.removeTab(tab);
+  BrowserTestUtils.removeTab(privateTab);
+  await BrowserTestUtils.closeWindow(privateWindow);
+}
+
+add_setup(async function () {
+  // Disable the fingerprinting randomization.
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["privacy.resistFingerprinting.randomization.enabled", false],
+      ["privacy.fingerprintingProtection", false],
+      ["privacy.fingerprintingProtection.pbmode", false],
+      ["privacy.resistFingerprinting", false],
+    ],
+  });
+
+  // Open a tab for extracting the canvas data in the worker.
+  const tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, emptyPage);
+
+  // Extract the original canvas data without random noise.
+  for (let test of TEST_CASES) {
+    let data = await runFunctionInWorker(
+      tab.linkedBrowser,
+      test.extractCanvasData
+    );
+    test.originalData = data[0];
+  }
+
+  BrowserTestUtils.removeTab(tab);
+});
+
+add_task(async function run_tests_with_randomization_enabled() {
+  await runTest(true);
+});
+
+add_task(async function run_tests_with_randomization_disabled() {
+  await runTest(false);
+});
diff --git a/toolkit/components/resistfingerprinting/tests/browser/browser_fingerprinting_randomization_key.js b/toolkit/components/resistfingerprinting/tests/browser/browser_fingerprinting_randomization_key.js
new file mode 100644
index 0000000000..5213ea277d
--- /dev/null
+++ b/toolkit/components/resistfingerprinting/tests/browser/browser_fingerprinting_randomization_key.js
@@ -0,0 +1,458 @@
+const TEST_DOMAIN = "https://example.com";
+const TEST_DOMAIN_ANOTHER = "https://example.org";
+const TEST_DOMAIN_THIRD = "https://example.net";
+
+const TEST_PAGE =
+  getRootDirectory(gTestPath).replace(
+    "chrome://mochitests/content",
+    TEST_DOMAIN
+  ) + "testPage.html";
+const TEST_DOMAIN_ANOTHER_PAGE =
+  getRootDirectory(gTestPath).replace(
+    "chrome://mochitests/content",
+    TEST_DOMAIN_ANOTHER
+  ) + "testPage.html";
+const TEST_DOMAIN_THIRD_PAGE =
+  getRootDirectory(gTestPath).replace(
+    "chrome://mochitests/content",
+    TEST_DOMAIN_THIRD
+  ) + "testPage.html";
+
+/**
+ * A helper function to get the random key in a hex string format and test if
+ * the random key works properly.
+ *
+ * @param {Browser} browser The browser element of the testing tab.
+ * @param {string} firstPartyDomain The first-party domain loaded on the tab
+ * @param {string} thirdPartyDomain The third-party domain to test
+ * @returns {string} The random key hex string
+ */
+async function getRandomKeyHexFromBrowser(
+  browser,
+  firstPartyDomain,
+  thirdPartyDomain
+) {
+  // Get the key from the cookieJarSettings of the browser element.
+  let key = browser.cookieJarSettings.fingerprintingRandomizationKey;
+  let keyHex = key.map(bytes => bytes.toString(16).padStart(2, "0")).join("");
+
+  // Get the key from the cookieJarSettings of the top-level document.
+  let keyTop = await SpecialPowers.spawn(browser, [], _ => {
+    return content.document.cookieJarSettings.fingerprintingRandomizationKey;
+  });
+  let keyTopHex = keyTop
+    .map(bytes => bytes.toString(16).padStart(2, "0"))
+    .join("");
+
+  is(
+    keyTopHex,
+    keyHex,
+    "The fingerprinting random key should match between the browser element and the top-level document."
+  );
+
+  // Get the key from the cookieJarSettings of an about:blank iframe.
+  let keyAboutBlank = await SpecialPowers.spawn(browser, [], async _ => {
+    let ifr = content.document.createElement("iframe");
+
+    let loaded = new content.Promise(resolve => {
+      ifr.onload = resolve;
+    });
+    content.document.body.appendChild(ifr);
+    ifr.src = "about:blank";
+
+    await loaded;
+
+    return SpecialPowers.spawn(ifr, [], _ => {
+      return content.document.cookieJarSettings.fingerprintingRandomizationKey;
+    });
+  });
+
+  let keyAboutBlankHex = keyAboutBlank
+    .map(bytes => bytes.toString(16).padStart(2, "0"))
+    .join("");
+  is(
+    keyAboutBlankHex,
+    keyHex,
+    "The fingerprinting random key should match between the browser element and the about:blank iframe document."
+  );
+
+  // Get the key from the cookieJarSettings of the javascript URL iframe
+  // document.
+  let keyJavascriptURL = await SpecialPowers.spawn(browser, [], async _ => {
+    let ifr = content.document.getElementById("testFrame");
+
+    return ifr.contentDocument.cookieJarSettings.fingerprintingRandomizationKey;
+  });
+
+  let keyJavascriptURLHex = keyJavascriptURL
+    .map(bytes => bytes.toString(16).padStart(2, "0"))
+    .join("");
+  is(
+    keyJavascriptURLHex,
+    keyHex,
+    "The fingerprinting random key should match between the browser element and the javascript URL iframe document."
+  );
+
+  // Get the key from the cookieJarSettings of an first-party iframe.
+  let keyFirstPartyFrame = await SpecialPowers.spawn(
+    browser,
+    [firstPartyDomain],
+    async domain => {
+      let ifr = content.document.createElement("iframe");
+
+      let loaded = new content.Promise(resolve => {
+        ifr.onload = resolve;
+      });
+      content.document.body.appendChild(ifr);
+      ifr.src = domain;
+
+      await loaded;
+
+      return SpecialPowers.spawn(ifr, [], _ => {
+        return content.document.cookieJarSettings
+          .fingerprintingRandomizationKey;
+      });
+    }
+  );
+
+  let keyFirstPartyFrameHex = keyFirstPartyFrame
+    .map(bytes => bytes.toString(16).padStart(2, "0"))
+    .join("");
+  is(
+    keyFirstPartyFrameHex,
+    keyHex,
+    "The fingerprinting random key should match between the browser element and the first-party iframe document."
+  );
+
+  // Get the key from the cookieJarSettings of an third-party iframe
+  let keyThirdPartyFrame = await SpecialPowers.spawn(
+    browser,
+    [thirdPartyDomain],
+    async domain => {
+      let ifr = content.document.createElement("iframe");
+
+      let loaded = new content.Promise(resolve => {
+        ifr.onload = resolve;
+      });
+      content.document.body.appendChild(ifr);
+      ifr.src = domain;
+
+      await loaded;
+
+      return SpecialPowers.spawn(ifr, [], _ => {
+        return content.document.cookieJarSettings
+          .fingerprintingRandomizationKey;
+      });
+    }
+  );
+
+  let keyThirdPartyFrameHex = keyThirdPartyFrame
+    .map(bytes => bytes.toString(16).padStart(2, "0"))
+    .join("");
+  is(
+    keyThirdPartyFrameHex,
+    keyHex,
+    "The fingerprinting random key should match between the browser element and the third-party iframe document."
+  );
+
+  return keyHex;
+}
+
+// Test accessing the fingerprinting randomization key will throw if
+// fingerprinting randomization is disabled.
+add_task(async function test_randomization_disabled() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["privacy.resistFingerprinting.randomization.enabled", false]],
+  });
+
+  // Ensure accessing the fingerprinting randomization key of the browser
+  // element will throw if fingerprinting randomization is disabled.
+  let tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, TEST_PAGE);
+
+  try {
+    let key =
+      tab.linkedBrowser.cookieJarSettings.fingerprintingRandomizationKey;
+    ok(
+      false,
+      `Accessing the fingerprinting randomization key should throw when randomization is disabled. ${key}`
+    );
+  } catch (e) {
+    ok(
+      true,
+      "It should throw when getting the key when randomization is disabled."
+    );
+  }
+
+  // Ensure accessing the fingerprinting randomization key of the top-level
+  // document will throw if fingerprinting randomization is disabled.
+  try {
+    await SpecialPowers.spawn(tab.linkedBrowser, [], _ => {
+      return content.document.cookieJarSettings.fingerprintingRandomizationKey;
+    });
+  } catch (e) {
+    ok(
+      true,
+      "It should throw when getting the key when randomization is disabled."
+    );
+  }
+
+  BrowserTestUtils.removeTab(tab);
+});
+
+// Test accessing the fingerprinting randomization key will throw if
+// fingerprinting resistance is disabled.
+add_task(async function test_randomization_disabled_with_rfp_disabled() {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["privacy.resistFingerprinting.randomization.enabled", true],
+      ["privacy.resistFingerprinting", false],
+    ],
+  });
+
+  // Ensure accessing the fingerprinting randomization key of the browser
+  // element will throw if fingerprinting randomization is disabled.
+  let tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, TEST_PAGE);
+
+  try {
+    let key =
+      tab.linkedBrowser.cookieJarSettings.fingerprintingRandomizationKey;
+    ok(
+      false,
+      `Accessing the fingerprinting randomization key should throw when fingerprinting resistance is disabled. ${key}`
+    );
+  } catch (e) {
+    ok(
+      true,
+      "It should throw when getting the key when fingerprinting resistance is disabled."
+    );
+  }
+
+  // Ensure accessing the fingerprinting randomization key of the top-level
+  // document will throw if fingerprinting randomization is disabled.
+  try {
+    await SpecialPowers.spawn(tab.linkedBrowser, [], _ => {
+      return content.document.cookieJarSettings.fingerprintingRandomizationKey;
+    });
+  } catch (e) {
+    ok(
+      true,
+      "It should throw when getting the key when fingerprinting resistance is disabled."
+    );
+  }
+
+  BrowserTestUtils.removeTab(tab);
+});
+
+// Test the fingerprinting randomization key generation.
+add_task(async function test_generate_randomization_key() {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["privacy.resistFingerprinting.randomization.enabled", true],
+      ["privacy.resistFingerprinting", true],
+    ],
+  });
+
+  for (let testPrivateWin of [true, false]) {
+    let win = window;
+
+    if (testPrivateWin) {
+      win = await BrowserTestUtils.openNewBrowserWindow({
+        private: true,
+      });
+    }
+
+    let tabOne = await BrowserTestUtils.openNewForegroundTab(
+      win.gBrowser,
+      TEST_PAGE
+    );
+    let keyHexOne;
+
+    try {
+      keyHexOne = await getRandomKeyHexFromBrowser(
+        tabOne.linkedBrowser,
+        TEST_PAGE,
+        TEST_DOMAIN_THIRD_PAGE
+      );
+      ok(true, `The fingerprinting random key: ${keyHexOne}`);
+    } catch (e) {
+      ok(
+        false,
+        "Shouldn't fail when getting the random key from the cookieJarSettings"
+      );
+    }
+
+    // Open the test domain again and check if the key remains the same.
+    let tabTwo = await BrowserTestUtils.openNewForegroundTab(
+      win.gBrowser,
+      TEST_PAGE
+    );
+    try {
+      let keyHexTwo = await getRandomKeyHexFromBrowser(
+        tabTwo.linkedBrowser,
+        TEST_PAGE,
+        TEST_DOMAIN_THIRD_PAGE
+      );
+      is(
+        keyHexTwo,
+        keyHexOne,
+        `The key should remain the same after reopening the tab.`
+      );
+    } catch (e) {
+      ok(
+        false,
+        "Shouldn't fail when getting the random key from the cookieJarSettings"
+      );
+    }
+
+    // Open a tab with a different domain to see if the key changes.
+    let tabAnother = await BrowserTestUtils.openNewForegroundTab(
+      win.gBrowser,
+      TEST_DOMAIN_ANOTHER_PAGE
+    );
+    try {
+      let keyHexAnother = await getRandomKeyHexFromBrowser(
+        tabAnother.linkedBrowser,
+        TEST_DOMAIN_ANOTHER_PAGE,
+        TEST_DOMAIN_THIRD_PAGE
+      );
+      isnot(
+        keyHexAnother,
+        keyHexOne,
+        `The key should be different when loading a different domain`
+      );
+    } catch (e) {
+      ok(
+        false,
+        "Shouldn't fail when getting the random key from the cookieJarSettings"
+      );
+    }
+
+    BrowserTestUtils.removeTab(tabOne);
+    BrowserTestUtils.removeTab(tabTwo);
+    BrowserTestUtils.removeTab(tabAnother);
+    if (testPrivateWin) {
+      await BrowserTestUtils.closeWindow(win);
+    }
+  }
+});
+
+// Test the fingerprinting randomization key will change after private session
+// ends.
+add_task(async function test_reset_key_after_pbm_session_ends() {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["privacy.resistFingerprinting.randomization.enabled", true],
+      ["privacy.resistFingerprinting", true],
+    ],
+  });
+
+  let privateWin = await BrowserTestUtils.openNewBrowserWindow({
+    private: true,
+  });
+
+  // Open a tab in the private window.
+  let tab = await BrowserTestUtils.openNewForegroundTab(
+    privateWin.gBrowser,
+    TEST_PAGE
+  );
+
+  let keyHex = await getRandomKeyHexFromBrowser(
+    tab.linkedBrowser,
+    TEST_PAGE,
+    TEST_DOMAIN_THIRD_PAGE
+  );
+
+  // Close the window and open another private window.
+  BrowserTestUtils.removeTab(tab);
+  await BrowserTestUtils.closeWindow(privateWin);
+
+  privateWin = await BrowserTestUtils.openNewBrowserWindow({
+    private: true,
+  });
+
+  // Open a tab again in the new private window.
+  tab = await BrowserTestUtils.openNewForegroundTab(
+    privateWin.gBrowser,
+    TEST_PAGE
+  );
+
+  let keyHexNew = await getRandomKeyHexFromBrowser(
+    tab.linkedBrowser,
+    TEST_PAGE,
+    TEST_DOMAIN_THIRD_PAGE
+  );
+
+  // Ensure the keys are different.
+  isnot(keyHexNew, keyHex, "Ensure the new key is different from the old one.");
+
+  BrowserTestUtils.removeTab(tab);
+  await BrowserTestUtils.closeWindow(privateWin);
+});
+
+// Test accessing the fingerprinting randomization key will throw in normal
+// windows if we exempt fingerprinting protection in normal windows.
+add_task(async function test_randomization_with_exempted_normal_window() {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["privacy.resistFingerprinting.randomization.enabled", true],
+      ["privacy.resistFingerprinting", true],
+      ["privacy.resistFingerprinting.testGranularityMask", 2],
+    ],
+  });
+
+  // Ensure accessing the fingerprinting randomization key of the browser
+  // element will throw if fingerprinting randomization is exempted from normal
+  // windows.
+  let tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, TEST_PAGE);
+
+  try {
+    let key =
+      tab.linkedBrowser.cookieJarSettings.fingerprintingRandomizationKey;
+    ok(
+      false,
+      `Accessing the fingerprinting randomization key should throw when fingerprinting resistance is exempted in normal windows. ${key}`
+    );
+  } catch (e) {
+    ok(
+      true,
+      "It should throw when getting the key when fingerprinting resistance is exempted in normal windows."
+    );
+  }
+
+  // Ensure accessing the fingerprinting randomization key of the top-level
+  // document will throw if fingerprinting randomization is exempted from normal
+  // windows.
+  try {
+    await SpecialPowers.spawn(tab.linkedBrowser, [], _ => {
+      return content.document.cookieJarSettings.fingerprintingRandomizationKey;
+    });
+  } catch (e) {
+    ok(
+      true,
+      "It should throw when getting the key when fingerprinting resistance is exempted in normal windows."
+    );
+  }
+
+  BrowserTestUtils.removeTab(tab);
+
+  // Open a private window and check the key can be accessed there.
+  let privateWin = await BrowserTestUtils.openNewBrowserWindow({
+    private: true,
+  });
+
+  // Open a tab in the private window.
+  tab = await BrowserTestUtils.openNewForegroundTab(
+    privateWin.gBrowser,
+    TEST_PAGE
+  );
+
+  // Access the key, this shouldn't throw an error.
+  await getRandomKeyHexFromBrowser(
+    tab.linkedBrowser,
+    TEST_PAGE,
+    TEST_DOMAIN_THIRD_PAGE
+  );
+
+  BrowserTestUtils.removeTab(tab);
+  await BrowserTestUtils.closeWindow(privateWin);
+});
diff --git a/toolkit/components/resistfingerprinting/tests/browser/empty.html b/toolkit/components/resistfingerprinting/tests/browser/empty.html
new file mode 100644
index 0000000000..4e59eed479
--- /dev/null
+++ b/toolkit/components/resistfingerprinting/tests/browser/empty.html
@@ -0,0 +1,8 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <title>An empty page for testing</title>
+</head>
+<body>
+</body>
+</html>
diff --git a/toolkit/components/resistfingerprinting/tests/browser/head.js b/toolkit/components/resistfingerprinting/tests/browser/head.js
new file mode 100644
index 0000000000..a5a0b7ef55
--- /dev/null
+++ b/toolkit/components/resistfingerprinting/tests/browser/head.js
@@ -0,0 +1,52 @@
+// Number of bits in the canvas that we randomize when canvas randomization is
+// enabled.
+const NUM_RANDOMIZED_CANVAS_BITS = 256;
+
+/**
+ * Compares two Uint8Arrays and returns the number of bits that are different.
+ *
+ * @param {Uint8ClampedArray} arr1 - The first Uint8ClampedArray to compare.
+ * @param {Uint8ClampedArray} arr2 - The second Uint8ClampedArray to compare.
+ * @returns {number} - The number of bits that are different between the two
+ *                     arrays.
+ */
+function compareUint8Arrays(arr1, arr2) {
+  let count = 0;
+  for (let i = 0; i < arr1.length; i++) {
+    let diff = arr1[i] ^ arr2[i];
+    while (diff > 0) {
+      count += diff & 1;
+      diff >>= 1;
+    }
+  }
+  return count;
+}
+
+/**
+ * Compares two ArrayBuffer objects to see if they are different.
+ *
+ * @param {ArrayBuffer} buffer1 - The first buffer to compare.
+ * @param {ArrayBuffer} buffer2 - The second buffer to compare.
+ * @returns {boolean} True if the buffers are different, false if they are the
+ *                    same.
+ */
+function compareArrayBuffer(buffer1, buffer2) {
+  // compare the byte lengths of the two buffers
+  if (buffer1.byteLength !== buffer2.byteLength) {
+    return true;
+  }
+
+  // create typed arrays to represent the two buffers
+  const view1 = new DataView(buffer1);
+  const view2 = new DataView(buffer2);
+
+  // compare the byte values of the two typed arrays
+  for (let i = 0; i < buffer1.byteLength; i++) {
+    if (view1.getUint8(i) !== view2.getUint8(i)) {
+      return true;
+    }
+  }
+
+  // the two buffers are the same
+  return false;
+}
diff --git a/toolkit/components/resistfingerprinting/tests/browser/testPage.html b/toolkit/components/resistfingerprinting/tests/browser/testPage.html
new file mode 100644
index 0000000000..07a17d3d71
--- /dev/null
+++ b/toolkit/components/resistfingerprinting/tests/browser/testPage.html
@@ -0,0 +1,9 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <title>A page with a javascript URL iframe</title>
+</head>
+<body>
+  <iframe id="testFrame" src="javascript:void(0)"></iframe>
+</body>
+</html>
diff --git a/toolkit/components/resistfingerprinting/tests/browser/worker.js b/toolkit/components/resistfingerprinting/tests/browser/worker.js
new file mode 100644
index 0000000000..894b208549
--- /dev/null
+++ b/toolkit/components/resistfingerprinting/tests/browser/worker.js
@@ -0,0 +1,7 @@
+onmessage = e => {
+  let runnableStr = `(() => {return (${e.data.callback});})();`;
+  let runnable = eval(runnableStr); // eslint-disable-line no-eval
+  runnable.call(this).then(result => {
+    postMessage({ result });
+  });
+};
diff --git a/toolkit/components/resistfingerprinting/tests/chrome.ini b/toolkit/components/resistfingerprinting/tests/chrome.ini
new file mode 100644
index 0000000000..ff7c487ab4
--- /dev/null
+++ b/toolkit/components/resistfingerprinting/tests/chrome.ini
@@ -0,0 +1,4 @@
+[DEFAULT]
+skip-if = os == 'android'
+
+[test_spoof_english.html]
diff --git a/toolkit/components/resistfingerprinting/tests/moz.build b/toolkit/components/resistfingerprinting/tests/moz.build
new file mode 100644
index 0000000000..f5c1582193
--- /dev/null
+++ b/toolkit/components/resistfingerprinting/tests/moz.build
@@ -0,0 +1,13 @@
+UNIFIED_SOURCES += [
+    "test_reduceprecision.cpp",
+]
+
+MOCHITEST_CHROME_MANIFESTS += [
+    "chrome.ini",
+]
+
+BROWSER_CHROME_MANIFESTS += [
+    "browser/browser.ini",
+]
+
+FINAL_LIBRARY = "xul-gtest"
diff --git a/toolkit/components/resistfingerprinting/tests/test_reduceprecision.cpp b/toolkit/components/resistfingerprinting/tests/test_reduceprecision.cpp
new file mode 100644
index 0000000000..4a2ec72b66
--- /dev/null
+++ b/toolkit/components/resistfingerprinting/tests/test_reduceprecision.cpp
@@ -0,0 +1,565 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: sw=2 ts=2 et lcs=trail\:.,tab\:>~ :
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * 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 <math.h>
+
+#include "gtest/gtest.h"
+#include "nsIPrefBranch.h"
+#include "nsIPrefService.h"
+#include "nsServiceManagerUtils.h"
+#include "nsRFPService.h"
+
+using namespace mozilla;
+
+// clang-format off
+/*
+   Hello! Are you looking at this file because you got an error you don't understand?
+   Perhaps something that looks like the following?
+
+    toolkit/components/resistfingerprinting/tests/test_reduceprecision.cpp:15: Failure
+      Expected: reduced1
+        Which is: 2064.83
+      To be equal to: reduced2
+        Which is: 2064.83
+
+   "Gosh," you might say, "They sure look equal to me. What the heck is going on here?"
+
+   The answer lies beyond what you can see, in that which you cannot see. One must
+   journey into the depths, the hidden, that which the world fights its hardest to
+   conceal from us.
+
+   Specially: you need to look at more decimal places. Run the test with:
+       MOZ_LOG="nsResistFingerprinting:5"
+
+   And look for two successive lines similar to the below (the format will certainly
+   be different by the time you read this comment):
+      V/nsResistFingerprinting Given: 2064.83384599999999, Reciprocal Rounding with 50000.00000000000000, Intermediate: 103241692.00000000000000, Got: 2064.83383999999978
+      V/nsResistFingerprinting Given: 2064.83383999999978, Reciprocal Rounding with 50000.00000000000000, Intermediate: 103241691.00000000000000, Got: 2064.83381999999983
+
+   Look at the last two values:
+      Got: 2064.83383999999978
+      Got: 2064.83381999999983
+
+   They're supposed to be equal. They're not. But they both round to 2064.83.
+*/
+// clang-format on
+
+bool setupJitter(bool enabled) {
+  nsCOMPtr<nsIPrefBranch> prefs = do_GetService(NS_PREFSERVICE_CONTRACTID);
+
+  bool jitterEnabled = false;
+  if (prefs) {
+    prefs->GetBoolPref(
+        "privacy.resistFingerprinting.reduceTimerPrecision.jitter",
+        &jitterEnabled);
+    prefs->SetBoolPref(
+        "privacy.resistFingerprinting.reduceTimerPrecision.jitter", enabled);
+  }
+
+  return jitterEnabled;
+}
+
+void cleanupJitter(bool jitterWasEnabled) {
+  nsCOMPtr<nsIPrefBranch> prefs = do_GetService(NS_PREFSERVICE_CONTRACTID);
+  if (prefs) {
+    prefs->SetBoolPref(
+        "privacy.resistFingerprinting.reduceTimerPrecision.jitter",
+        jitterWasEnabled);
+  }
+}
+
+void process(double clock, nsRFPService::TimeScale clockUnits,
+             double precision) {
+  double reduced1 = nsRFPService::ReduceTimePrecisionImpl(
+      clock, clockUnits, precision, -1, TimerPrecisionType::Normal);
+  double reduced2 = nsRFPService::ReduceTimePrecisionImpl(
+      reduced1, clockUnits, precision, -1, TimerPrecisionType::Normal);
+  ASSERT_EQ(reduced1, reduced2);
+}
+
+TEST(ResistFingerprinting, ReducePrecision_Assumptions)
+{
+  ASSERT_EQ(FLT_RADIX, 2);
+  ASSERT_EQ(DBL_MANT_DIG, 53);
+}
+
+TEST(ResistFingerprinting, ReducePrecision_Reciprocal)
+{
+  bool jitterEnabled = setupJitter(false);
+  // This one has a rounding error in the Reciprocal case:
+  process(2064.8338460, nsRFPService::TimeScale::MicroSeconds, 20);
+  // These are just big values
+  process(1516305819, nsRFPService::TimeScale::MicroSeconds, 20);
+  process(69053.12, nsRFPService::TimeScale::MicroSeconds, 20);
+  cleanupJitter(jitterEnabled);
+}
+
+TEST(ResistFingerprinting, ReducePrecision_KnownGood)
+{
+  bool jitterEnabled = setupJitter(false);
+  process(2064.8338460, nsRFPService::TimeScale::MilliSeconds, 20);
+  process(69027.62, nsRFPService::TimeScale::MilliSeconds, 20);
+  process(69053.12, nsRFPService::TimeScale::MilliSeconds, 20);
+  cleanupJitter(jitterEnabled);
+}
+
+TEST(ResistFingerprinting, ReducePrecision_KnownBad)
+{
+  bool jitterEnabled = setupJitter(false);
+  process(1054.842405, nsRFPService::TimeScale::MilliSeconds, 20);
+  process(273.53038600000002, nsRFPService::TimeScale::MilliSeconds, 20);
+  process(628.66686500000003, nsRFPService::TimeScale::MilliSeconds, 20);
+  process(521.28919100000007, nsRFPService::TimeScale::MilliSeconds, 20);
+  cleanupJitter(jitterEnabled);
+}
+
+TEST(ResistFingerprinting, ReducePrecision_Edge)
+{
+  bool jitterEnabled = setupJitter(false);
+  process(2611.14, nsRFPService::TimeScale::MilliSeconds, 20);
+  process(2611.16, nsRFPService::TimeScale::MilliSeconds, 20);
+  process(2612.16, nsRFPService::TimeScale::MilliSeconds, 20);
+  process(2601.64, nsRFPService::TimeScale::MilliSeconds, 20);
+  process(2595.16, nsRFPService::TimeScale::MilliSeconds, 20);
+  process(2578.66, nsRFPService::TimeScale::MilliSeconds, 20);
+  cleanupJitter(jitterEnabled);
+}
+
+TEST(ResistFingerprinting, ReducePrecision_Expectations)
+{
+  bool jitterEnabled = setupJitter(false);
+  double result;
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      2611.14, nsRFPService::TimeScale::MilliSeconds, 20, -1,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 2611.14);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      2611.145, nsRFPService::TimeScale::MilliSeconds, 20, -1,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 2611.14);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      2611.141, nsRFPService::TimeScale::MilliSeconds, 20, -1,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 2611.14);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      2611.15999, nsRFPService::TimeScale::MilliSeconds, 20, -1,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 2611.14);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      2611.15, nsRFPService::TimeScale::MilliSeconds, 20, -1,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 2611.14);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      2611.13, nsRFPService::TimeScale::MilliSeconds, 20, -1,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 2611.12);
+  cleanupJitter(jitterEnabled);
+}
+
+TEST(ResistFingerprinting, ReducePrecision_Expectations_HighRes)
+{
+  bool jitterEnabled = setupJitter(false);
+  double result;
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      2611.14, nsRFPService::TimeScale::MilliSeconds, 20, -1,
+      TimerPrecisionType::UnconditionalAKAHighRes);
+  ASSERT_EQ(result, 2611.14);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      2611.145, nsRFPService::TimeScale::MilliSeconds, 20, -1,
+      TimerPrecisionType::UnconditionalAKAHighRes);
+  ASSERT_EQ(result, 2611.14);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      2611.141, nsRFPService::TimeScale::MilliSeconds, 20, -1,
+      TimerPrecisionType::UnconditionalAKAHighRes);
+  ASSERT_EQ(result, 2611.14);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      2611.15999, nsRFPService::TimeScale::MilliSeconds, 20, -1,
+      TimerPrecisionType::UnconditionalAKAHighRes);
+  ASSERT_EQ(result, 2611.14);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      2611.15, nsRFPService::TimeScale::MilliSeconds, 20, -1,
+      TimerPrecisionType::UnconditionalAKAHighRes);
+  ASSERT_EQ(result, 2611.14);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      2611.13, nsRFPService::TimeScale::MilliSeconds, 20, -1,
+      TimerPrecisionType::UnconditionalAKAHighRes);
+  ASSERT_EQ(result, 2611.12);
+  cleanupJitter(jitterEnabled);
+}
+
+TEST(ResistFingerprinting, ReducePrecision_Expectations_RFP)
+{
+  bool jitterEnabled = setupJitter(false);
+  double result;
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      2611.14, nsRFPService::TimeScale::MilliSeconds, 20, -1,
+      TimerPrecisionType::RFP);
+  ASSERT_EQ(result, 2611.14);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      2611.145, nsRFPService::TimeScale::MilliSeconds, 20, -1,
+      TimerPrecisionType::RFP);
+  ASSERT_EQ(result, 2611.14);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      2611.141, nsRFPService::TimeScale::MilliSeconds, 20, -1,
+      TimerPrecisionType::RFP);
+  ASSERT_EQ(result, 2611.14);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      2611.15999, nsRFPService::TimeScale::MilliSeconds, 20, -1,
+      TimerPrecisionType::RFP);
+  ASSERT_EQ(result, 2611.14);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      2611.15, nsRFPService::TimeScale::MilliSeconds, 20, -1,
+      TimerPrecisionType::RFP);
+  ASSERT_EQ(result, 2611.14);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      2611.13, nsRFPService::TimeScale::MilliSeconds, 20, -1,
+      TimerPrecisionType::RFP);
+  ASSERT_EQ(result, 2611.12);
+  cleanupJitter(jitterEnabled);
+}
+
+TEST(ResistFingerprinting, ReducePrecision_Expectations_DangerouslyNone)
+{
+  bool jitterEnabled = setupJitter(false);
+  double result;
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      2611.14, nsRFPService::TimeScale::MilliSeconds, 20, -1,
+      TimerPrecisionType::DangerouslyNone);
+  ASSERT_EQ(result, 2611.14);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      2611.145, nsRFPService::TimeScale::MilliSeconds, 20, -1,
+      TimerPrecisionType::DangerouslyNone);
+  ASSERT_EQ(result, 2611.145);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      2611.141, nsRFPService::TimeScale::MilliSeconds, 20, -1,
+      TimerPrecisionType::DangerouslyNone);
+  ASSERT_EQ(result, 2611.141);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      2611.15999, nsRFPService::TimeScale::MilliSeconds, 20, -1,
+      TimerPrecisionType::DangerouslyNone);
+  ASSERT_EQ(result, 2611.15999);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      2611.15, nsRFPService::TimeScale::MilliSeconds, 20, -1,
+      TimerPrecisionType::DangerouslyNone);
+  ASSERT_EQ(result, 2611.15);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      2611.13, nsRFPService::TimeScale::MilliSeconds, 20, -1,
+      TimerPrecisionType::DangerouslyNone);
+  ASSERT_EQ(result, 2611.13);
+  cleanupJitter(jitterEnabled);
+}
+
+TEST(ResistFingerprinting, ReducePrecision_ExpectedLossOfPrecision)
+{
+  bool jitterEnabled = setupJitter(false);
+  double result;
+  // We lose integer precision at 9007199254740992 - let's confirm that.
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      9007199254740992.0, nsRFPService::TimeScale::MicroSeconds, 5, -1,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 9007199254740990.0);
+  // 9007199254740995 is approximated to 9007199254740996
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      9007199254740995.0, nsRFPService::TimeScale::MicroSeconds, 5, -1,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 9007199254740996);
+  // 9007199254740999 is approximated as 9007199254741000
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      9007199254740999.0, nsRFPService::TimeScale::MicroSeconds, 5, -1,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 9007199254741000.0);
+  // 9007199254743568 can be represented exactly, but will be clamped to
+  // 9007199254743564
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      9007199254743568.0, nsRFPService::TimeScale::MicroSeconds, 5, -1,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 9007199254743564.0);
+  cleanupJitter(jitterEnabled);
+}
+
+TEST(ResistFingerprinting, ReducePrecision_ExpectedLossOfPrecision_HighRes)
+{
+  bool jitterEnabled = setupJitter(false);
+  double result;
+  // We lose integer precision at 9007199254740992 - let's confirm that.
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      9007199254740992.0, nsRFPService::TimeScale::MicroSeconds, 5, -1,
+      TimerPrecisionType::UnconditionalAKAHighRes);
+  ASSERT_EQ(result, 9007199254740980.0);
+  // 9007199254740995 is approximated to 9007199254740980
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      9007199254740995.0, nsRFPService::TimeScale::MicroSeconds, 5, -1,
+      TimerPrecisionType::UnconditionalAKAHighRes);
+  ASSERT_EQ(result, 9007199254740980);
+  // 9007199254740999 is approximated as 9007199254741000
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      9007199254740999.0, nsRFPService::TimeScale::MicroSeconds, 5, -1,
+      TimerPrecisionType::UnconditionalAKAHighRes);
+  ASSERT_EQ(result, 9007199254741000.0);
+  // 9007199254743568 can be represented exactly, but will be clamped to
+  // 9007199254743560
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      9007199254743568.0, nsRFPService::TimeScale::MicroSeconds, 5, -1,
+      TimerPrecisionType::UnconditionalAKAHighRes);
+  ASSERT_EQ(result, 9007199254743560.0);
+  cleanupJitter(jitterEnabled);
+}
+
+TEST(ResistFingerprinting, ReducePrecision_ExpectedLossOfPrecision_RFP)
+{
+  bool jitterEnabled = setupJitter(false);
+  double result;
+  // We lose integer precision at 9007199254740992 - let's confirm that.
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      9007199254740992.0, nsRFPService::TimeScale::MicroSeconds, 5, -1,
+      TimerPrecisionType::RFP);
+  ASSERT_EQ(result, 9007199254740990.0);
+  // 9007199254740995 is approximated to 9007199254740980
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      9007199254740995.0, nsRFPService::TimeScale::MicroSeconds, 5, -1,
+      TimerPrecisionType::RFP);
+  ASSERT_EQ(result, 9007199254740995);
+  // 9007199254740999 is approximated as 9007199254741000
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      9007199254740999.0, nsRFPService::TimeScale::MicroSeconds, 5, -1,
+      TimerPrecisionType::RFP);
+  ASSERT_EQ(result, 9007199254741000.0);
+  // 9007199254743568 can be represented exactly, but will be clamped to
+  // 9007199254743560
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      9007199254743568.0, nsRFPService::TimeScale::MicroSeconds, 5, -1,
+      TimerPrecisionType::RFP);
+  ASSERT_EQ(result, 9007199254743565.0);
+  cleanupJitter(jitterEnabled);
+}
+
+TEST(ResistFingerprinting,
+     ReducePrecision_ExpectedLossOfPrecision_DangerouslyNone)
+{
+  bool jitterEnabled = setupJitter(false);
+  double result;
+  // We lose integer precision at 9007199254740992 - let's confirm that.
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      9007199254740992.0, nsRFPService::TimeScale::MicroSeconds, 5, -1,
+      TimerPrecisionType::DangerouslyNone);
+  ASSERT_EQ(result, 9007199254740992.0);
+  // 9007199254740995 is approximated to 9007199254740980
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      9007199254740995.0, nsRFPService::TimeScale::MicroSeconds, 5, -1,
+      TimerPrecisionType::DangerouslyNone);
+  ASSERT_EQ(result, 9007199254740995);
+  // 9007199254740999 is approximated as 9007199254741000
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      9007199254740999.0, nsRFPService::TimeScale::MicroSeconds, 5, -1,
+      TimerPrecisionType::DangerouslyNone);
+  ASSERT_EQ(result, 9007199254740999.0);
+  // 9007199254743568 can be represented exactly, but will be clamped to
+  // 9007199254743560
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      9007199254743568.0, nsRFPService::TimeScale::MicroSeconds, 5, -1,
+      TimerPrecisionType::DangerouslyNone);
+  ASSERT_EQ(result, 9007199254743568.0);
+  cleanupJitter(jitterEnabled);
+}
+
+// Use an ugly but simple hack to turn an integer-based rand()
+// function to a double-based one.
+#define RAND_DOUBLE (rand() * (rand() / (double)rand()))
+
+// If you're doing logging, you really don't want to run this test.
+#define RUN_AGGRESSIVE false
+
+TEST(ResistFingerprinting, ReducePrecision_Aggressive)
+{
+  if (!RUN_AGGRESSIVE) {
+    return;
+  }
+
+  bool jitterEnabled = setupJitter(false);
+
+  for (int i = 0; i < 10000; i++) {
+    // Test three different time magnitudes, with decimals.
+    // Note that we need separate variables for the different units, as scaling
+    // them after calculating them will erase effects of approximation.
+    // A magnitude in the seconds since epoch range.
+    double time1_s = fmod(RAND_DOUBLE, 1516305819.0);
+    double time1_ms = fmod(RAND_DOUBLE, 1516305819000.0);
+    double time1_us = fmod(RAND_DOUBLE, 1516305819000000.0);
+    // A magnitude in the 'couple of minutes worth of milliseconds' range.
+    double time2_s = fmod(RAND_DOUBLE, (60.0 * 60 * 5));
+    double time2_ms = fmod(RAND_DOUBLE, (1000.0 * 60 * 60 * 5));
+    double time2_us = fmod(RAND_DOUBLE, (1000000.0 * 60 * 60 * 5));
+    // A magnitude in the small range
+    double time3_s = fmod(RAND_DOUBLE, 10);
+    double time3_ms = fmod(RAND_DOUBLE, 10000);
+    double time3_us = fmod(RAND_DOUBLE, 10000000);
+
+    // Test two precision magnitudes, no decimals.
+    // A magnitude in the high milliseconds.
+    double precision1 = rand() % 250000;
+    // a magnitude in the low microseconds.
+    double precision2 = rand() % 200;
+
+    process(time1_s, nsRFPService::TimeScale::Seconds, precision1);
+    process(time1_s, nsRFPService::TimeScale::Seconds, precision2);
+    process(time2_s, nsRFPService::TimeScale::Seconds, precision1);
+    process(time2_s, nsRFPService::TimeScale::Seconds, precision2);
+    process(time3_s, nsRFPService::TimeScale::Seconds, precision1);
+    process(time3_s, nsRFPService::TimeScale::Seconds, precision2);
+
+    process(time1_ms, nsRFPService::TimeScale::MilliSeconds, precision1);
+    process(time1_ms, nsRFPService::TimeScale::MilliSeconds, precision2);
+    process(time2_ms, nsRFPService::TimeScale::MilliSeconds, precision1);
+    process(time2_ms, nsRFPService::TimeScale::MilliSeconds, precision2);
+    process(time3_ms, nsRFPService::TimeScale::MilliSeconds, precision1);
+    process(time3_ms, nsRFPService::TimeScale::MilliSeconds, precision2);
+
+    process(time1_us, nsRFPService::TimeScale::MicroSeconds, precision1);
+    process(time1_us, nsRFPService::TimeScale::MicroSeconds, precision2);
+    process(time2_us, nsRFPService::TimeScale::MicroSeconds, precision1);
+    process(time2_us, nsRFPService::TimeScale::MicroSeconds, precision2);
+    process(time3_us, nsRFPService::TimeScale::MicroSeconds, precision1);
+    process(time3_us, nsRFPService::TimeScale::MicroSeconds, precision2);
+  }
+  cleanupJitter(jitterEnabled);
+}
+
+TEST(ResistFingerprinting, ReducePrecision_JitterTestVectors)
+{
+  bool jitterEnabled = setupJitter(true);
+
+  // clang-format off
+  /*
+   * Here's our test vector. We set the secret to the 16 byte value
+   * 0x0001020304050607 0x1011121314151617
+   *
+   * We then use a stand alone XOrShift128+ generator:
+   *
+   * The midpoints are:
+   *   0    = 328
+   *   500  = 25
+   *   1000 = 73
+   *   1500 = 89
+   *   2000 = 73
+   *   2500 = 153
+   *   3000 = 9
+   *   3500 = 89
+   *   4000 = 73
+   *   4500 = 205
+   *   5000 = 253
+   *   5500 = 141
+   */
+  // clang-format on
+
+  // Set the secret
+  long long throwAway;
+  uint8_t hardcodedSecret[16] = {0x00, 0x01, 0x02, 0x03, 0x04, 0x05,
+                                 0x06, 0x07, 0x10, 0x11, 0x12, 0x13,
+                                 0x14, 0x15, 0x16, 0x17};
+
+  nsRFPService::RandomMidpoint(0, 500, -1, &throwAway, hardcodedSecret);
+
+  // Run the test vectors
+  double result;
+
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      1, nsRFPService::TimeScale::MicroSeconds, 500, 4000,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 0);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      184, nsRFPService::TimeScale::MicroSeconds, 500, 4000,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 0);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      185, nsRFPService::TimeScale::MicroSeconds, 500, 4000,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 500);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      329, nsRFPService::TimeScale::MicroSeconds, 500, 4000,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 500);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      499, nsRFPService::TimeScale::MicroSeconds, 500, 4000,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 500);
+
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      500, nsRFPService::TimeScale::MicroSeconds, 500, 4000,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 500);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      520, nsRFPService::TimeScale::MicroSeconds, 500, 4000,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 500);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      524, nsRFPService::TimeScale::MicroSeconds, 500, 4000,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 500);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      525, nsRFPService::TimeScale::MicroSeconds, 500, 4000,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 1000);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      930, nsRFPService::TimeScale::MicroSeconds, 500, 4000,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 1000);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      1072, nsRFPService::TimeScale::MicroSeconds, 500, 4000,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 1000);
+
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      4000, nsRFPService::TimeScale::MicroSeconds, 500, 4000,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 4000);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      4050, nsRFPService::TimeScale::MicroSeconds, 500, 4000,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 4000);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      4072, nsRFPService::TimeScale::MicroSeconds, 500, 4000,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 4000);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      4073, nsRFPService::TimeScale::MicroSeconds, 500, 4000,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 4500);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      4340, nsRFPService::TimeScale::MicroSeconds, 500, 4000,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 4500);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      4499, nsRFPService::TimeScale::MicroSeconds, 500, 4000,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 4500);
+
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      4500, nsRFPService::TimeScale::MicroSeconds, 500, 4000,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 4500);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      4536, nsRFPService::TimeScale::MicroSeconds, 500, 4000,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 4500);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      4704, nsRFPService::TimeScale::MicroSeconds, 500, 4000,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 4500);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      4705, nsRFPService::TimeScale::MicroSeconds, 500, 4000,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 5000);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      4726, nsRFPService::TimeScale::MicroSeconds, 500, 4000,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 5000);
+  result = nsRFPService::ReduceTimePrecisionImpl(
+      5106, nsRFPService::TimeScale::MicroSeconds, 500, 4000,
+      TimerPrecisionType::Normal);
+  ASSERT_EQ(result, 5000);
+
+  cleanupJitter(jitterEnabled);
+}
diff --git a/toolkit/components/resistfingerprinting/tests/test_spoof_english.html b/toolkit/components/resistfingerprinting/tests/test_spoof_english.html
new file mode 100644
index 0000000000..1ebc6277e9
--- /dev/null
+++ b/toolkit/components/resistfingerprinting/tests/test_spoof_english.html
@@ -0,0 +1,119 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1486258
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1486258</title>
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="chrome://global/skin"/>
+  <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1486258">Mozilla Bug 1486258</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+
+<script type="text/javascript">
+/* global SpecialPowers */
+
+const { BrowserTestUtils } = ChromeUtils.import("resource://testing-common/BrowserTestUtils.jsm");
+;
+
+const gOrigAvailableLocales = Services.locale.availableLocales;
+const gOrigRequestedLocales = Services.locale.requestedLocales;
+
+const kDoNotSpoof = 1;
+const kSpoofEnglish = 2;
+
+async function runTest(locale) {
+  return BrowserTestUtils.withNewTab("http://example.com/", browser => {
+    return SpecialPowers.spawn(browser, [locale], _locale => {
+      return {
+        locale: new Intl.PluralRules(_locale).resolvedOptions().locale,
+        weekday: new Date(0).toLocaleString(_locale, {weekday: "long"}),
+        currency: Number(1000).toLocaleString(_locale, {currency: "USD"}),
+      };
+    });
+  });
+}
+
+async function runSpoofTest(spoof) {
+  ok(spoof == kDoNotSpoof ||
+     spoof == kSpoofEnglish, "check supported parameter");
+
+  await SpecialPowers.pushPrefEnv({
+    "set": [
+      ["privacy.spoof_english", spoof],
+    ],
+  });
+
+  is(SpecialPowers.getBoolPref("javascript.use_us_english_locale", false),
+     spoof == kSpoofEnglish,
+     "use_us_english_locale");
+
+  let results = await runTest(undefined);
+
+  await SpecialPowers.popPrefEnv();
+
+  return results;
+}
+
+async function setupLocale(locale) {
+  Services.locale.availableLocales = [locale];
+  Services.locale.requestedLocales = [locale];
+}
+
+async function clearLocale() {
+  Services.locale.availableLocales = gOrigAvailableLocales;
+  Services.locale.requestedLocales = gOrigRequestedLocales;
+}
+
+(async function() {
+  SimpleTest.waitForExplicitFinish();
+
+  // 1. preliminary for spoof test
+  await SpecialPowers.pushPrefEnv({
+    "set": [
+      ["privacy.resistFingerprinting", true],
+    ],
+  });
+
+  // 2. log English/German results
+  let enResults = await runTest("en-US");
+  is(enResults.locale, "en-US", "default locale");
+
+  let deResults = await runTest("de");
+  is(deResults.locale, "de", "default locale");
+
+  // 3. set system locale to German
+  await setupLocale("de");
+
+  // 4. log non-spoofed results
+  let nonSpoofedResults = await runSpoofTest(kDoNotSpoof);
+
+  // 5. log spoofed results
+  let spoofedResults = await runSpoofTest(kSpoofEnglish);
+
+  // 6. compare spoofed/non-spoofed results
+  for (let key in enResults) {
+    isnot(enResults[key], deResults[key], "compare en/de result: " + key);
+    is(nonSpoofedResults[key], deResults[key], "compare non-spoofed result: " + key);
+    is(spoofedResults[key], enResults[key], "compare spoofed result: " + key);
+  }
+
+  // 7. restore default locale
+  await clearLocale();
+
+  SimpleTest.finish();
+})();
+
+</script>
+
+</body>
+</html>