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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* 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 */
#include "PreferenceSheet.h"
#include "ServoCSSParser.h"
#include "MainThreadUtils.h"
#include "mozilla/Encoding.h"
#include "mozilla/Preferences.h"
#include "mozilla/StaticPrefs_browser.h"
#include "mozilla/StaticPrefs_layout.h"
#include "mozilla/StaticPrefs_widget.h"
#include "mozilla/StaticPrefs_ui.h"
#include "mozilla/Telemetry.h"
#include "mozilla/LookAndFeel.h"
#include "mozilla/ServoBindings.h"
#include "mozilla/dom/Document.h"
#include "nsContentUtils.h"
#define AVG2(a, b) (((a) + (b) + 1) >> 1)
namespace mozilla {
using dom::Document;
bool PreferenceSheet::sInitialized;
PreferenceSheet::Prefs PreferenceSheet::sContentPrefs;
PreferenceSheet::Prefs PreferenceSheet::sChromePrefs;
PreferenceSheet::Prefs PreferenceSheet::sPrintPrefs;
static void GetColor(const char* aPrefName, ColorScheme aColorScheme,
nscolor& aColor) {
nsAutoCString darkPrefName;
if (aColorScheme == ColorScheme::Dark) {
aPrefName = darkPrefName.get();
nsAutoCString value;
Preferences::GetCString(aPrefName, value);
if (value.IsEmpty() || Encoding::UTF8ValidUpTo(value) != value.Length()) {
nscolor result;
if (!ServoCSSParser::ComputeColor(nullptr, NS_RGB(0, 0, 0), value, &result)) {
aColor = result;
auto PreferenceSheet::PrefsKindFor(const Document& aDoc) -> PrefsKind {
if (aDoc.IsInChromeDocShell()) {
return PrefsKind::Chrome;
if (aDoc.IsBeingUsedAsImage() && aDoc.ChromeRulesEnabled()) {
return PrefsKind::Chrome;
if (aDoc.IsStaticDocument()) {
return PrefsKind::Print;
return PrefsKind::Content;
static bool UseDocumentColors(bool aUseAcccessibilityTheme) {
switch (StaticPrefs::browser_display_document_color_use()) {
case 1:
return true;
case 2:
return false;
return !aUseAcccessibilityTheme;
static bool UseStandinsForNativeColors() {
return nsContentUtils::ShouldResistFingerprinting(
"we want to have consistent colors across the browser if RFP is "
"enabled, so we check the global preference"
"not excluding chrome browsers or webpages, so we call the legacy "
"RFP function to prevent that",
RFPTarget::UseStandinsForNativeColors) ||
void PreferenceSheet::Prefs::LoadColors(bool aIsLight) {
auto& colors = aIsLight ? mLightColors : mDarkColors;
if (!aIsLight) {
// Initialize the dark-color-scheme foreground/background colors as being
// the reverse of these members' default values, for ~reasonable fallback if
// the user configures broken pref values.
std::swap(colors.mDefault, colors.mDefaultBackground);
const auto scheme = aIsLight ? ColorScheme::Light : ColorScheme::Dark;
// Link colors might be provided by the OS, but they might not be. If they are
// not, then fall back to the pref colors.
// In particular, we don't query active link color to the OS.
GetColor("browser.anchor_color", scheme, colors.mLink);
GetColor("browser.active_color", scheme, colors.mActiveLink);
GetColor("browser.visited_color", scheme, colors.mVisitedLink);
// Historically we've given more weight to the "use standins" setting than the
// "use system colors" one. In practice most users don't use standins because
// it's hidden behind prefs.
if (mUsePrefColors && !mUseStandins) {
GetColor("browser.display.background_color", scheme,
GetColor("browser.display.foreground_color", scheme, colors.mDefault);
} else {
using ColorID = LookAndFeel::ColorID;
const auto standins = LookAndFeel::UseStandins(mUseStandins);
colors.mDefault = LookAndFeel::Color(ColorID::Windowtext, scheme, standins,
colors.mDefaultBackground = LookAndFeel::Color(
ColorID::Window, scheme, standins, colors.mDefaultBackground);
colors.mLink = LookAndFeel::Color(ColorID::MozNativehyperlinktext, scheme,
standins, colors.mLink);
if (auto color = LookAndFeel::GetColor(
ColorID::MozNativevisitedhyperlinktext, scheme, standins)) {
// If the system provides a visited link color, we should use it.
colors.mVisitedLink = *color;
} else if (mUseAccessibilityTheme) {
// The fallback visited link color on HCM (if the system doesn't provide
// one) is produced by preserving the foreground's green and averaging the
// foreground and background for the red and blue. This is how IE and
// Edge do it too.
colors.mVisitedLink = NS_RGB(
AVG2(NS_GET_R(colors.mDefault), NS_GET_R(colors.mDefaultBackground)),
AVG2(NS_GET_B(colors.mDefault), NS_GET_B(colors.mDefaultBackground)));
} else {
// Otherwise we keep the default visited link color
if (mUseAccessibilityTheme) {
colors.mActiveLink = colors.mLink;
// Wherever we got the default background color from, ensure it is opaque.
colors.mDefaultBackground =
NS_ComposeColors(NS_RGB(0xFF, 0xFF, 0xFF), colors.mDefaultBackground);
bool PreferenceSheet::Prefs::NonNativeThemeShouldBeHighContrast() const {
// We only do that if we are overriding the document colors. Otherwise it
// causes issues when pages only override some of the system colors,
// specially in dark themes mode.
return StaticPrefs::widget_non_native_theme_always_high_contrast() ||
auto PreferenceSheet::ColorSchemeSettingForChrome()
-> ChromeColorSchemeSetting {
switch (StaticPrefs::browser_theme_toolbar_theme()) {
case 0: // Dark
return ChromeColorSchemeSetting::Dark;
case 1: // Light
return ChromeColorSchemeSetting::Light;
return ChromeColorSchemeSetting::System;
ColorScheme PreferenceSheet::ThemeDerivedColorSchemeForContent() {
switch (StaticPrefs::browser_theme_content_theme()) {
case 0: // Dark
return ColorScheme::Dark;
case 1: // Light
return ColorScheme::Light;
return LookAndFeel::SystemColorScheme();
void PreferenceSheet::Prefs::Load(bool aIsChrome) {
*this = {};
mIsChrome = aIsChrome;
mUseAccessibilityTheme =
// Chrome documents always use system colors, not stand-ins, not forced, etc.
if (!aIsChrome) {
mUseDocumentColors = UseDocumentColors(mUseAccessibilityTheme);
mUsePrefColors = !StaticPrefs::browser_display_use_system_colors();
mUseStandins = UseStandinsForNativeColors();
// When forcing the pref colors, we need to forcibly use the light color-set,
// as those are the colors exposed to the user in the colors dialog.
mMustUseLightColorSet = mUsePrefColors && !mUseDocumentColors;
#ifdef XP_WIN
if (mUseAccessibilityTheme && (mIsChrome || !mUseDocumentColors)) {
// Windows overrides the light colors with the HCM colors when HCM is
// active, so make sure to always use the light system colors in that case,
// and also make sure that we always use the light color set for the same
// reason.
mMustUseLightSystemColors = mMustUseLightColorSet = true;
mColorScheme = [&] {
if (aIsChrome) {
switch (ColorSchemeSettingForChrome()) {
case ChromeColorSchemeSetting::Light:
return ColorScheme::Light;
case ChromeColorSchemeSetting::Dark:
return ColorScheme::Dark;
case ChromeColorSchemeSetting::System:
return LookAndFeel::SystemColorScheme();
if (mMustUseLightColorSet) {
// When forcing colors in a way such as color-scheme isn't respected, we
// compute a preference based on the darkness of
// our background.
return LookAndFeel::IsDarkColor(mLightColors.mDefaultBackground)
? ColorScheme::Dark
: ColorScheme::Light;
switch (StaticPrefs::layout_css_prefers_color_scheme_content_override()) {
case 0:
return ColorScheme::Dark;
case 1:
return ColorScheme::Light;
return ThemeDerivedColorSchemeForContent();
void PreferenceSheet::Initialize() {
sInitialized = true;
sPrintPrefs = sContentPrefs;
// For printing, we always use a preferred-light color scheme.
sPrintPrefs.mColorScheme = ColorScheme::Light;
if (!sPrintPrefs.mUseDocumentColors) {
// When overriding document colors, we ignore the `color-scheme` property,
// but we still don't want to use the system colors (which might be dark,
// despite having made it into mLightColors), because it both wastes ink
// and it might interact poorly with the color adjustments we do while
// printing.
// So we override the light colors with our hardcoded default colors, and
// force the use of stand-ins.
sPrintPrefs.mLightColors = Prefs().mLightColors;
sPrintPrefs.mUseStandins = true;
nsAutoString useDocumentColorPref;
switch (StaticPrefs::browser_display_document_color_use()) {
case 1:
case 2:
Telemetry::ScalarSet(Telemetry::ScalarID::A11Y_THEME, useDocumentColorPref,
if (!sContentPrefs.mUseDocumentColors) {
// If a user has chosen to override doc colors through OS HCM or our HCM,
// we should log the user's current foreground (text) color and background
// color. Note, the document color use pref is the inverse of the HCM
// dropdown option in preferences.
// Note that we only look at light colors because that's the color set we
// use when forcing colors (since color-scheme is ignored when colors are
// forced).
// The light color set is the one that potentially contains the Windows HCM
// theme color/background (if we're using system colors and the user is
// using a High Contrast theme), and also the colors that as of today we
// allow setting in about:preferences.
bool PreferenceSheet::AffectedByPref(const nsACString& aPref) {
const char* prefNames[] = {
if (StringBeginsWith(aPref, "browser.display."_ns)) {
return true;
for (const char* pref : prefNames) {
if (aPref.Equals(pref)) {
return true;
return false;
} // namespace mozilla
#undef AVG2