Merging upstream version 127.0.

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

19 files changed, 277 insertions, 234 deletions

diff --git a/dom/svg/SVGAElement.cpp b/dom/svg/SVGAElement.cpp
index 1533cceb34..bffc3d1a98 100644
--- a/dom/svg/SVGAElement.cpp
+++ b/dom/svg/SVGAElement.cpp
@@ -6,11 +6,10 @@
 
 #include "mozilla/dom/SVGAElement.h"
 
-#include "mozilla/Attributes.h"
 #include "mozilla/EventDispatcher.h"
-#include "mozilla/dom/BindContext.h"
 #include "mozilla/dom/DocumentInlines.h"
 #include "mozilla/dom/SVGAElementBinding.h"
+#include "mozilla/FocusModel.h"
 #include "nsCOMPtr.h"
 #include "nsContentUtils.h"
 #include "nsGkAtoms.h"
@@ -158,7 +157,7 @@ void SVGAElement::UnbindFromTree(UnbindContext& aContext) {
 
 int32_t SVGAElement::TabIndexDefault() { return 0; }
 
-Focusable SVGAElement::IsFocusableWithoutStyle(bool aWithMouse) {
+Focusable SVGAElement::IsFocusableWithoutStyle(IsFocusableFlags) {
   Focusable result;
   if (IsSVGFocusable(&result.mFocusable, &result.mTabIndex)) {
     return result;
@@ -182,7 +181,7 @@ Focusable SVGAElement::IsFocusableWithoutStyle(bool aWithMouse) {
       return {};
     }
   }
-  if ((sTabFocusModel & eTabFocus_linksMask) == 0) {
+  if (!FocusModel::IsTabFocusable(TabFocusableType::Links)) {
     result.mTabIndex = -1;
   }
   return result;
diff --git a/dom/svg/SVGAElement.h b/dom/svg/SVGAElement.h
index bbb552fce6..5e476c033c 100644
--- a/dom/svg/SVGAElement.h
+++ b/dom/svg/SVGAElement.h
@@ -50,7 +50,7 @@ class SVGAElement final : public SVGAElementBase, public Link {
   void UnbindFromTree(UnbindContext&) override;
 
   int32_t TabIndexDefault() override;
-  Focusable IsFocusableWithoutStyle(bool aWithMouse) override;
+  Focusable IsFocusableWithoutStyle(IsFocusableFlags) override;
 
   void GetLinkTarget(nsAString& aTarget) override;
   already_AddRefed<nsIURI> GetHrefURI() const override;
diff --git a/dom/svg/SVGAnimatedLength.cpp b/dom/svg/SVGAnimatedLength.cpp
index 081db5704a..156fde0e23 100644
--- a/dom/svg/SVGAnimatedLength.cpp
+++ b/dom/svg/SVGAnimatedLength.cpp
@@ -225,6 +225,10 @@ CSSSize SVGElementMetrics::GetCSSViewportSize() const {
   return GetCSSViewportSizeFromContext(context);
 }
 
+float SVGElementMetrics::GetLineHeight(Type aType) const {
+  return SVGContentUtils::GetLineHeight(GetElementForType(aType));
+}
+
 bool SVGElementMetrics::EnsureCtx() const {
   if (!mCtx && mSVGElement) {
     mCtx = mSVGElement->GetCtx();
@@ -298,6 +302,23 @@ CSSSize NonSVGFrameUserSpaceMetrics::GetCSSViewportSize() const {
   return GetCSSViewportSizeFromContext(mFrame->PresContext());
 }
 
+float NonSVGFrameUserSpaceMetrics::GetLineHeight(Type aType) const {
+  auto* context = mFrame->PresContext();
+  switch (aType) {
+    case Type::This: {
+      const auto lineHeightAu = ReflowInput::CalcLineHeight(
+          *mFrame->Style(), context, mFrame->GetContent(), NS_UNCONSTRAINEDSIZE,
+          1.0f);
+      return CSSPixel::FromAppUnits(lineHeightAu);
+    }
+    case Type::Root:
+      return SVGContentUtils::GetLineHeight(
+          context->Document()->GetRootElement());
+  }
+  MOZ_ASSERT_UNREACHABLE("Was a new value added to the enumeration?");
+  return 1.0f;
+}
+
 float UserSpaceMetricsWithSize::GetAxisLength(uint8_t aCtxType) const {
   gfx::Size size = GetSize();
   float length;
diff --git a/dom/svg/SVGAnimatedLength.h b/dom/svg/SVGAnimatedLength.h
index 6874261cda..0e5c228667 100644
--- a/dom/svg/SVGAnimatedLength.h
+++ b/dom/svg/SVGAnimatedLength.h
@@ -53,6 +53,7 @@ class UserSpaceMetrics {
   float GetCapHeight(Type aType) const;
   virtual float GetAxisLength(uint8_t aCtxType) const = 0;
   virtual CSSSize GetCSSViewportSize() const = 0;
+  virtual float GetLineHeight(Type aType) const = 0;
 
  protected:
   virtual GeckoFontMetrics GetFontMetricsForType(Type aType) const = 0;
@@ -75,6 +76,7 @@ class SVGElementMetrics : public UserSpaceMetrics {
   }
   float GetAxisLength(uint8_t aCtxType) const override;
   CSSSize GetCSSViewportSize() const override;
+  float GetLineHeight(Type aType) const override;
 
  private:
   bool EnsureCtx() const;
@@ -93,6 +95,7 @@ class NonSVGFrameUserSpaceMetrics : public UserSpaceMetricsWithSize {
   float GetEmLength(Type aType) const override;
   gfx::Size GetSize() const override;
   CSSSize GetCSSViewportSize() const override;
+  float GetLineHeight(Type aType) const override;
 
  private:
   GeckoFontMetrics GetFontMetricsForType(Type aType) const override;
diff --git a/dom/svg/SVGContentUtils.cpp b/dom/svg/SVGContentUtils.cpp
index 72534c12e8..6a87c64acc 100644
--- a/dom/svg/SVGContentUtils.cpp
+++ b/dom/svg/SVGContentUtils.cpp
@@ -433,6 +433,26 @@ float SVGContentUtils::GetFontXHeight(const ComputedStyle* aComputedStyle,
   return nsPresContext::AppUnitsToFloatCSSPixels(xHeight) /
          aPresContext->TextZoom();
 }
+
+float SVGContentUtils::GetLineHeight(const Element* aElement) {
+  float result = 16.0f * ReflowInput::kNormalLineHeightFactor;
+  if (!aElement) {
+    return result;
+  }
+  SVGGeometryProperty::DoForComputedStyle(
+      aElement, [&](const ComputedStyle* style) {
+        auto* context = nsContentUtils::GetContextForContent(aElement);
+        if (!context) {
+          return;
+        }
+        const auto lineHeightAu = ReflowInput::CalcLineHeight(
+            *style, context, aElement, NS_UNCONSTRAINEDSIZE, 1.0f);
+        result = CSSPixel::FromAppUnits(lineHeightAu);
+      });
+
+  return result;
+}
+
 nsresult SVGContentUtils::ReportToConsole(const Document* doc,
                                           const char* aWarning,
                                           const nsTArray<nsString>& aParams) {
@@ -596,8 +616,12 @@ static gfx::Matrix GetCTMInternal(SVGElement* aElement, bool aScreenCTM,
              : tm;
 }
 
-gfx::Matrix SVGContentUtils::GetCTM(SVGElement* aElement, bool aScreenCTM) {
-  return GetCTMInternal(aElement, aScreenCTM, false);
+gfx::Matrix SVGContentUtils::GetCTM(SVGElement* aElement) {
+  return GetCTMInternal(aElement, false, false);
+}
+
+gfx::Matrix SVGContentUtils::GetScreenCTM(SVGElement* aElement) {
+  return GetCTMInternal(aElement, true, false);
 }
 
 void SVGContentUtils::RectilinearGetStrokeBounds(
diff --git a/dom/svg/SVGContentUtils.h b/dom/svg/SVGContentUtils.h
index 8cd017b709..31e75cbb21 100644
--- a/dom/svg/SVGContentUtils.h
+++ b/dom/svg/SVGContentUtils.h
@@ -180,13 +180,24 @@ class SVGContentUtils {
   static float GetFontXHeight(const ComputedStyle*, nsPresContext*);
 
   /*
+   * Get the number of CSS px (user units) per lh (i.e. the line-height in
+   * user units) for an nsIContent.
+   *
+   * Requires the element be styled - if not, a default value assuming
+   * the font-size of 16px and line-height of 1.2 is returned.
+   */
+  static float GetLineHeight(const mozilla::dom::Element* aElement);
+
+  /*
    * Report a localized error message to the error console.
    */
   static nsresult ReportToConsole(const dom::Document* doc,
                                   const char* aWarning,
                                   const nsTArray<nsString>& aParams);
 
-  static Matrix GetCTM(dom::SVGElement* aElement, bool aScreenCTM);
+  static Matrix GetCTM(dom::SVGElement* aElement);
+
+  static Matrix GetScreenCTM(dom::SVGElement* aElement);
 
   /**
    * Gets the tight bounds-space stroke bounds of the non-scaling-stroked rect
diff --git a/dom/svg/SVGDefsElement.h b/dom/svg/SVGDefsElement.h
index 38f6d4fab9..55c2c8fb95 100644
--- a/dom/svg/SVGDefsElement.h
+++ b/dom/svg/SVGDefsElement.h
@@ -25,7 +25,7 @@ class SVGDefsElement final : public SVGGraphicsElement {
 
  public:
   // defs elements are not focusable.
-  Focusable IsFocusableWithoutStyle(bool aWithMouse) override { return {}; }
+  Focusable IsFocusableWithoutStyle(IsFocusableFlags) override { return {}; }
   nsresult Clone(dom::NodeInfo*, nsINode** aResult) const override;
 };
 
diff --git a/dom/svg/SVGGeometryElement.cpp b/dom/svg/SVGGeometryElement.cpp
index de5756ed7d..149dae8ba4 100644
--- a/dom/svg/SVGGeometryElement.cpp
+++ b/dom/svg/SVGGeometryElement.cpp
@@ -201,7 +201,7 @@ bool SVGGeometryElement::IsPointInStroke(const DOMPointInit& aPoint) {
   SVGGeometryProperty::DoForComputedStyle(this, [&](const ComputedStyle* s) {
     // Per spec, we should take vector-effect into account.
     if (s->StyleSVGReset()->HasNonScalingStroke()) {
-      auto mat = SVGContentUtils::GetCTM(this, true);
+      auto mat = SVGContentUtils::GetCTM(this);
       if (mat.HasNonTranslation()) {
         // We have non-scaling-stroke as well as a non-translation transform.
         // We should transform the path first then apply the stroke on the
diff --git a/dom/svg/SVGGraphicsElement.cpp b/dom/svg/SVGGraphicsElement.cpp
index 29b6b76728..52bb023e61 100644
--- a/dom/svg/SVGGraphicsElement.cpp
+++ b/dom/svg/SVGGraphicsElement.cpp
@@ -129,7 +129,7 @@ already_AddRefed<SVGMatrix> SVGGraphicsElement::GetCTM() {
     // Flush all pending notifications so that our frames are up to date
     currentDoc->FlushPendingNotifications(FlushType::Layout);
   }
-  gfx::Matrix m = SVGContentUtils::GetCTM(this, false);
+  gfx::Matrix m = SVGContentUtils::GetCTM(this);
   RefPtr<SVGMatrix> mat =
       m.IsSingular() ? nullptr : new SVGMatrix(ThebesMatrix(m));
   return mat.forget();
@@ -140,7 +140,7 @@ already_AddRefed<SVGMatrix> SVGGraphicsElement::GetScreenCTM() {
     // Flush all pending notifications so that our frames are up to date
     currentDoc->FlushPendingNotifications(FlushType::Layout);
   }
-  gfx::Matrix m = SVGContentUtils::GetCTM(this, true);
+  gfx::Matrix m = SVGContentUtils::GetScreenCTM(this);
   RefPtr<SVGMatrix> mat =
       m.IsSingular() ? nullptr : new SVGMatrix(ThebesMatrix(m));
   return mat.forget();
@@ -164,7 +164,7 @@ bool SVGGraphicsElement::IsSVGFocusable(bool* aIsFocusable,
   return false;
 }
 
-Focusable SVGGraphicsElement::IsFocusableWithoutStyle(bool aWithMouse) {
+Focusable SVGGraphicsElement::IsFocusableWithoutStyle(IsFocusableFlags) {
   Focusable result;
   IsSVGFocusable(&result.mFocusable, &result.mTabIndex);
   return result;
diff --git a/dom/svg/SVGGraphicsElement.h b/dom/svg/SVGGraphicsElement.h
index 610436d394..1c5be3e324 100644
--- a/dom/svg/SVGGraphicsElement.h
+++ b/dom/svg/SVGGraphicsElement.h
@@ -34,7 +34,7 @@ class SVGGraphicsElement : public SVGGraphicsElementBase, public SVGTests {
   already_AddRefed<SVGMatrix> GetCTM();
   already_AddRefed<SVGMatrix> GetScreenCTM();
 
-  Focusable IsFocusableWithoutStyle(bool aWithMouse) override;
+  Focusable IsFocusableWithoutStyle(IsFocusableFlags) override;
   bool IsSVGGraphicsElement() const final { return true; }
 
   using nsINode::Clone;
diff --git a/dom/svg/SVGLength.cpp b/dom/svg/SVGLength.cpp
index f7c383a16f..bbe01e6878 100644
--- a/dom/svg/SVGLength.cpp
+++ b/dom/svg/SVGLength.cpp
@@ -20,15 +20,19 @@ using namespace mozilla::dom::SVGLength_Binding;
 
 namespace mozilla {
 
+// These types are numbered so that different length categories are in
+// contiguous ranges - See `SVGLength::Is[..]Unit()`.
 const unsigned short SVG_LENGTHTYPE_Q = 11;
 const unsigned short SVG_LENGTHTYPE_CH = 12;
 const unsigned short SVG_LENGTHTYPE_REM = 13;
 const unsigned short SVG_LENGTHTYPE_IC = 14;
 const unsigned short SVG_LENGTHTYPE_CAP = 15;
-const unsigned short SVG_LENGTHTYPE_VW = 16;
-const unsigned short SVG_LENGTHTYPE_VH = 17;
-const unsigned short SVG_LENGTHTYPE_VMIN = 18;
-const unsigned short SVG_LENGTHTYPE_VMAX = 19;
+const unsigned short SVG_LENGTHTYPE_LH = 16;
+const unsigned short SVG_LENGTHTYPE_RLH = 17;
+const unsigned short SVG_LENGTHTYPE_VW = 18;
+const unsigned short SVG_LENGTHTYPE_VH = 19;
+const unsigned short SVG_LENGTHTYPE_VMIN = 20;
+const unsigned short SVG_LENGTHTYPE_VMAX = 21;
 
 void SVGLength::GetValueAsString(nsAString& aValue) const {
   nsTextFormatter::ssprintf(aValue, u"%g", (double)mValue);
@@ -74,7 +78,7 @@ bool SVGLength::IsAbsoluteUnit(uint8_t aUnit) {
 /*static*/
 bool SVGLength::IsFontRelativeUnit(uint8_t aUnit) {
   return aUnit == SVG_LENGTHTYPE_EMS || aUnit == SVG_LENGTHTYPE_EXS ||
-         (aUnit >= SVG_LENGTHTYPE_CH && aUnit <= SVG_LENGTHTYPE_CAP);
+         (aUnit >= SVG_LENGTHTYPE_CH && aUnit <= SVG_LENGTHTYPE_RLH);
 }
 
 /**
@@ -192,6 +196,10 @@ float SVGLength::GetPixelsPerUnit(const UserSpaceMetrics& aMetrics,
       auto sz = aMetrics.GetCSSViewportSize();
       return std::max(sz.width, sz.height) / 100.f;
     }
+    case SVG_LENGTHTYPE_LH:
+      return aMetrics.GetLineHeight(UserSpaceMetrics::Type::This);
+    case SVG_LENGTHTYPE_RLH:
+      return aMetrics.GetLineHeight(UserSpaceMetrics::Type::Root);
     default:
       MOZ_ASSERT(IsAbsoluteUnit(aUnitType));
       return GetAbsUnitsPerAbsUnit(SVG_LENGTHTYPE_PX, aUnitType);
@@ -256,6 +264,12 @@ nsCSSUnit SVGLength::SpecifiedUnitTypeToCSSUnit(uint8_t aSpecifiedUnit) {
     case SVG_LENGTHTYPE_VMAX:
       return nsCSSUnit::eCSSUnit_VMax;
 
+    case SVG_LENGTHTYPE_LH:
+      return nsCSSUnit::eCSSUnit_LineHeight;
+
+    case SVG_LENGTHTYPE_RLH:
+      return nsCSSUnit::eCSSUnit_RootLineHeight;
+
     default:
       MOZ_ASSERT_UNREACHABLE("Unknown unit type");
       return nsCSSUnit::eCSSUnit_Pixel;
@@ -322,6 +336,12 @@ void SVGLength::GetUnitString(nsAString& aUnit, uint16_t aUnitType) {
     case SVG_LENGTHTYPE_VMAX:
       aUnit.AssignLiteral("vmax");
       return;
+    case SVG_LENGTHTYPE_LH:
+      aUnit.AssignLiteral("lh");
+      return;
+    case SVG_LENGTHTYPE_RLH:
+      aUnit.AssignLiteral("rlh");
+      return;
   }
   MOZ_ASSERT_UNREACHABLE(
       "Unknown unit type! Someone's using an SVGLength "
@@ -387,6 +407,12 @@ uint16_t SVGLength::GetUnitTypeForString(const nsAString& aUnit) {
   if (aUnit.LowerCaseEqualsLiteral("vmax")) {
     return SVG_LENGTHTYPE_VMAX;
   }
+  if (aUnit.LowerCaseEqualsLiteral("lh")) {
+    return SVG_LENGTHTYPE_LH;
+  }
+  if (aUnit.LowerCaseEqualsLiteral("rlh")) {
+    return SVG_LENGTHTYPE_RLH;
+  }
   return SVG_LENGTHTYPE_UNKNOWN;
 }
 
diff --git a/dom/svg/SVGSwitchElement.cpp b/dom/svg/SVGSwitchElement.cpp
index e049d07496..a19dfd8631 100644
--- a/dom/svg/SVGSwitchElement.cpp
+++ b/dom/svg/SVGSwitchElement.cpp
@@ -7,7 +7,6 @@
 #include "mozilla/dom/SVGSwitchElement.h"
 
 #include "nsLayoutUtils.h"
-#include "mozilla/Preferences.h"
 #include "mozilla/SVGUtils.h"
 #include "mozilla/dom/SVGSwitchElementBinding.h"
 
@@ -46,14 +45,13 @@ void SVGSwitchElement::MaybeInvalidate() {
   // InvalidateAndScheduleBoundsUpdate has been called, otherwise
   // it will not correctly invalidate the old mActiveChild area.
 
-  nsIContent* newActiveChild = FindActiveChild();
+  auto* newActiveChild = SVGTests::FindActiveSwitchChild(this);
 
   if (newActiveChild == mActiveChild) {
     return;
   }
 
-  nsIFrame* frame = GetPrimaryFrame();
-  if (frame) {
+  if (auto* frame = GetPrimaryFrame()) {
     nsLayoutUtils::PostRestyleEvent(this, RestyleHint{0},
                                     nsChangeHint_InvalidateRenderingObservers);
     SVGUtils::ScheduleReflowSVG(frame);
@@ -86,54 +84,4 @@ void SVGSwitchElement::RemoveChildNode(nsIContent* aKid, bool aNotify) {
   MaybeInvalidate();
 }
 
-//----------------------------------------------------------------------
-// Implementation Helpers:
-
-nsIContent* SVGSwitchElement::FindActiveChild() const {
-  nsAutoString acceptLangs;
-  Preferences::GetLocalizedString("intl.accept_languages", acceptLangs);
-
-  int32_t bestLanguagePreferenceRank = -1;
-  nsIContent* bestChild = nullptr;
-  nsIContent* defaultChild = nullptr;
-  for (nsIContent* child = nsINode::GetFirstChild(); child;
-       child = child->GetNextSibling()) {
-    if (!child->IsElement()) {
-      continue;
-    }
-    nsCOMPtr<SVGTests> tests(do_QueryInterface(child));
-    if (tests) {
-      if (tests->PassesConditionalProcessingTestsIgnoringSystemLanguage()) {
-        int32_t languagePreferenceRank =
-            tests->GetBestLanguagePreferenceRank(acceptLangs);
-        switch (languagePreferenceRank) {
-          case 0:
-            // best possible match
-            return child;
-          case -1:
-            // no match
-            break;
-          case -2:
-            // no systemLanguage attribute. If there's nothing better
-            // we'll use the first such child.
-            if (!defaultChild) {
-              defaultChild = child;
-            }
-            break;
-          default:
-            if (bestLanguagePreferenceRank == -1 ||
-                languagePreferenceRank < bestLanguagePreferenceRank) {
-              bestLanguagePreferenceRank = languagePreferenceRank;
-              bestChild = child;
-            }
-            break;
-        }
-      }
-    } else if (!bestChild) {
-      bestChild = child;
-    }
-  }
-  return bestChild ? bestChild : defaultChild;
-}
-
 }  // namespace mozilla::dom
diff --git a/dom/svg/SVGSwitchElement.h b/dom/svg/SVGSwitchElement.h
index c244c0fe51..68c22e8f71 100644
--- a/dom/svg/SVGSwitchElement.h
+++ b/dom/svg/SVGSwitchElement.h
@@ -50,9 +50,6 @@ class SVGSwitchElement final : public SVGSwitchElementBase {
   nsresult Clone(dom::NodeInfo*, nsINode** aResult) const override;
 
  private:
-  void UpdateActiveChild() { mActiveChild = FindActiveChild(); }
-  nsIContent* FindActiveChild() const;
-
   // only this child will be displayed
   nsCOMPtr<nsIContent> mActiveChild;
 };
diff --git a/dom/svg/SVGSymbolElement.cpp b/dom/svg/SVGSymbolElement.cpp
index eec7851de3..26d8a04ff0 100644
--- a/dom/svg/SVGSymbolElement.cpp
+++ b/dom/svg/SVGSymbolElement.cpp
@@ -29,11 +29,11 @@ SVGSymbolElement::SVGSymbolElement(
     already_AddRefed<mozilla::dom::NodeInfo>&& aNodeInfo)
     : SVGSymbolElementBase(std::move(aNodeInfo)) {}
 
-Focusable SVGSymbolElement::IsFocusableWithoutStyle(bool aWithMouse) {
+Focusable SVGSymbolElement::IsFocusableWithoutStyle(IsFocusableFlags aFlags) {
   if (!CouldBeRendered()) {
     return {};
   }
-  return SVGSymbolElementBase::IsFocusableWithoutStyle(aWithMouse);
+  return SVGSymbolElementBase::IsFocusableWithoutStyle(aFlags);
 }
 
 bool SVGSymbolElement::CouldBeRendered() const {
diff --git a/dom/svg/SVGSymbolElement.h b/dom/svg/SVGSymbolElement.h
index 4f49775de2..9f5b59db41 100644
--- a/dom/svg/SVGSymbolElement.h
+++ b/dom/svg/SVGSymbolElement.h
@@ -26,7 +26,7 @@ class SVGSymbolElement final : public SVGSymbolElementBase {
   ~SVGSymbolElement() = default;
   JSObject* WrapNode(JSContext* cx, JS::Handle<JSObject*> aGivenProto) override;
 
-  Focusable IsFocusableWithoutStyle(bool aWithMouse) override;
+  Focusable IsFocusableWithoutStyle(IsFocusableFlags) override;
 
  public:
   // interfaces:
diff --git a/dom/svg/SVGTests.cpp b/dom/svg/SVGTests.cpp
index 6603663445..058065618e 100644
--- a/dom/svg/SVGTests.cpp
+++ b/dom/svg/SVGTests.cpp
@@ -5,12 +5,13 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "mozilla/dom/SVGTests.h"
+
 #include "DOMSVGStringList.h"
+#include "nsCharSeparatedTokenizer.h"
 #include "nsIContent.h"
 #include "nsIContentInlines.h"
 #include "mozilla/dom/SVGSwitchElement.h"
-#include "nsCharSeparatedTokenizer.h"
-#include "nsStyleUtil.h"
+#include "mozilla/intl/oxilangtag_ffi_generated.h"
 #include "mozilla/Preferences.h"
 
 namespace mozilla::dom {
@@ -58,39 +59,84 @@ bool SVGTests::IsConditionalProcessingAttribute(
   return false;
 }
 
-int32_t SVGTests::GetBestLanguagePreferenceRank(
-    const nsAString& aAcceptLangs) const {
-  if (!mStringListAttributes[LANGUAGE].IsExplicitlySet()) {
-    return -2;
+// Find the best match from aAvailLangs for the users accept-languages,
+// returning the index in the aAvailLangs list, or -1 if no match.
+int32_t FindBestLanguage(const nsTArray<nsCString>& aAvailLangs) {
+  AutoTArray<nsCString, 16> reqLangs;
+  nsCString acceptLangs;
+  Preferences::GetLocalizedCString("intl.accept_languages", acceptLangs);
+  nsCCharSeparatedTokenizer languageTokenizer(acceptLangs, ',');
+  while (languageTokenizer.hasMoreTokens()) {
+    reqLangs.AppendElement(languageTokenizer.nextToken());
   }
 
-  int32_t lowestRank = -1;
-
-  for (uint32_t i = 0; i < mStringListAttributes[LANGUAGE].Length(); i++) {
-    int32_t index = 0;
-    for (const nsAString& languageToken :
-         nsCharSeparatedTokenizer(aAcceptLangs, ',').ToRange()) {
-      bool exactMatch = languageToken.Equals(mStringListAttributes[LANGUAGE][i],
-                                             nsCaseInsensitiveStringComparator);
-      bool prefixOnlyMatch =
-          !exactMatch && nsStyleUtil::DashMatchCompare(
-                             mStringListAttributes[LANGUAGE][i], languageToken,
-                             nsCaseInsensitiveStringComparator);
-      if (index == 0 && exactMatch) {
-        // best possible match
-        return 0;
+  for (const auto& req : reqLangs) {
+    for (const auto& avail : aAvailLangs) {
+      if (avail.Length() > req.Length()) {
+        // Ensure that en does not match en-us, i.e. you need to have en in
+        // intl.accept_languages to match en in markup.
+        continue;
       }
-      if ((exactMatch || prefixOnlyMatch) &&
-          (lowestRank == -1 || 2 * index + prefixOnlyMatch < lowestRank)) {
-        lowestRank = 2 * index + prefixOnlyMatch;
+      using namespace intl::ffi;
+      struct LangTagDelete {
+        void operator()(LangTag* aLangTag) const { lang_tag_destroy(aLangTag); }
+      };
+      UniquePtr<LangTag, LangTagDelete> langTag(lang_tag_new(&avail));
+      if (langTag && lang_tag_matches(langTag.get(), &req)) {
+        return &avail - &aAvailLangs[0];
       }
-      ++index;
     }
   }
-  return lowestRank;
+  return -1;
 }
 
-bool SVGTests::PassesConditionalProcessingTestsIgnoringSystemLanguage() const {
+nsIContent* SVGTests::FindActiveSwitchChild(
+    const dom::SVGSwitchElement* aSwitch) {
+  AutoTArray<nsCString, 16> availLocales;
+  AutoTArray<nsIContent*, 16> children;
+  nsIContent* defaultChild = nullptr;
+  for (auto* child = aSwitch->GetFirstChild(); child;
+       child = child->GetNextSibling()) {
+    if (!child->IsElement()) {
+      continue;
+    }
+    nsCOMPtr<SVGTests> tests(do_QueryInterface(child));
+    if (tests) {
+      if (!tests->mPassesConditionalProcessingTests.valueOr(true) ||
+          !tests->PassesRequiredExtensionsTests()) {
+        continue;
+      }
+      const auto& languages = tests->mStringListAttributes[LANGUAGE];
+      if (!languages.IsExplicitlySet()) {
+        if (!defaultChild) {
+          defaultChild = child;
+        }
+        continue;
+      }
+      for (uint32_t i = 0; i < languages.Length(); i++) {
+        children.AppendElement(child);
+        availLocales.AppendElement(NS_ConvertUTF16toUTF8(languages[i]));
+      }
+    }
+  }
+
+  // For each entry in availLocales, we expect to have a corresponding entry
+  // in children that provides the child node associated with that locale.
+  MOZ_ASSERT(children.Length() == availLocales.Length());
+
+  if (availLocales.IsEmpty()) {
+    return defaultChild;
+  }
+
+  int32_t index = FindBestLanguage(availLocales);
+  if (index >= 0) {
+    return children[index];
+  }
+
+  return defaultChild;
+}
+
+bool SVGTests::PassesRequiredExtensionsTests() const {
   // Required Extensions
   //
   // The requiredExtensions  attribute defines a list of required language
@@ -98,12 +144,15 @@ bool SVGTests::PassesConditionalProcessingTestsIgnoringSystemLanguage() const {
   // go beyond the feature set defined in the SVG specification.
   // Each extension is identified by a URI reference.
   // For now, claim that mozilla's SVG implementation supports XHTML and MathML.
-  if (mStringListAttributes[EXTENSIONS].IsExplicitlySet()) {
-    if (mStringListAttributes[EXTENSIONS].IsEmpty()) {
+  const auto& extensions = mStringListAttributes[EXTENSIONS];
+  if (extensions.IsExplicitlySet()) {
+    if (extensions.IsEmpty()) {
+      mPassesConditionalProcessingTests = Some(false);
       return false;
     }
-    for (uint32_t i = 0; i < mStringListAttributes[EXTENSIONS].Length(); i++) {
-      if (!HasExtension(mStringListAttributes[EXTENSIONS][i])) {
+    for (uint32_t i = 0; i < extensions.Length(); i++) {
+      if (!HasExtension(extensions[i])) {
+        mPassesConditionalProcessingTests = Some(false);
         return false;
       }
     }
@@ -112,45 +161,36 @@ bool SVGTests::PassesConditionalProcessingTestsIgnoringSystemLanguage() const {
 }
 
 bool SVGTests::PassesConditionalProcessingTests() const {
-  if (!PassesConditionalProcessingTestsIgnoringSystemLanguage()) {
+  if (mPassesConditionalProcessingTests) {
+    return mPassesConditionalProcessingTests.value();
+  }
+  if (!PassesRequiredExtensionsTests()) {
     return false;
   }
 
   // systemLanguage
   //
-  // Evaluates to "true" if one of the languages indicated by user preferences
-  // exactly equals one of the languages given in the value of this parameter,
-  // or if one of the languages indicated by user preferences exactly equals a
-  // prefix of one of the languages given in the value of this parameter such
-  // that the first tag character following the prefix is "-".
-  if (mStringListAttributes[LANGUAGE].IsExplicitlySet()) {
-    if (mStringListAttributes[LANGUAGE].IsEmpty()) {
+  // Evaluates to true if there's a BCP 47 match for the one of the user
+  // preference languages with one of the languages given in the value of
+  // this parameter.
+  const auto& languages = mStringListAttributes[LANGUAGE];
+  if (languages.IsExplicitlySet()) {
+    if (languages.IsEmpty()) {
+      mPassesConditionalProcessingTests = Some(false);
       return false;
     }
 
-    // Get our language preferences
-    nsAutoString acceptLangs;
-    Preferences::GetLocalizedString("intl.accept_languages", acceptLangs);
-
-    if (acceptLangs.IsEmpty()) {
-      NS_WARNING(
-          "no default language specified for systemLanguage conditional test");
-      return false;
+    AutoTArray<nsCString, 4> availLocales;
+    for (uint32_t i = 0; i < languages.Length(); i++) {
+      availLocales.AppendElement(NS_ConvertUTF16toUTF8(languages[i]));
     }
 
-    for (uint32_t i = 0; i < mStringListAttributes[LANGUAGE].Length(); i++) {
-      nsCharSeparatedTokenizer languageTokenizer(acceptLangs, ',');
-      while (languageTokenizer.hasMoreTokens()) {
-        if (nsStyleUtil::DashMatchCompare(mStringListAttributes[LANGUAGE][i],
-                                          languageTokenizer.nextToken(),
-                                          nsCaseInsensitiveStringComparator)) {
-          return true;
-        }
-      }
-    }
-    return false;
+    mPassesConditionalProcessingTests =
+        Some(FindBestLanguage(availLocales) >= 0);
+    return mPassesConditionalProcessingTests.value();
   }
 
+  mPassesConditionalProcessingTests = Some(true);
   return true;
 }
 
@@ -163,6 +203,7 @@ bool SVGTests::ParseConditionalProcessingAttribute(nsAtom* aAttribute,
       if (NS_FAILED(rv)) {
         mStringListAttributes[i].Clear();
       }
+      mPassesConditionalProcessingTests = Nothing();
       MaybeInvalidate();
       return true;
     }
@@ -174,6 +215,7 @@ void SVGTests::UnsetAttr(const nsAtom* aAttribute) {
   for (uint32_t i = 0; i < ArrayLength(sStringListNames); i++) {
     if (aAttribute == sStringListNames[i]) {
       mStringListAttributes[i].Clear();
+      mPassesConditionalProcessingTests = Nothing();
       MaybeInvalidate();
       return;
     }
diff --git a/dom/svg/SVGTests.h b/dom/svg/SVGTests.h
index 148c35fc5c..90991fd60d 100644
--- a/dom/svg/SVGTests.h
+++ b/dom/svg/SVGTests.h
@@ -13,13 +13,15 @@
 
 class nsAttrValue;
 class nsAtom;
+class nsIContent;
 class nsStaticAtom;
 
 namespace mozilla {
 
 namespace dom {
 class DOMSVGStringList;
-}
+class SVGSwitchElement;
+}  // namespace dom
 
 #define MOZILLA_DOMSVGTESTS_IID                      \
   {                                                  \
@@ -42,26 +44,10 @@ class SVGTests : public nsISupports {
   using SVGStringList = mozilla::SVGStringList;
 
   /**
-   * Compare the language name(s) in a systemLanguage attribute to the
-   * user's language preferences, as defined in
-   * http://www.w3.org/TR/SVG11/struct.html#SystemLanguageAttribute
-   * We have a match if a language name in the users language preferences
-   * exactly equals one of the language names or exactly equals a prefix of
-   * one of the language names in the systemLanguage attribute.
-   * @returns 2 * the lowest index in the aAcceptLangs that matches + 1
-   * if only the prefix matches, -2 if there's no systemLanguage attribute,
-   * or -1 if no indices match.
-   * XXX This algorithm is O(M*N).
-   */
-  int32_t GetBestLanguagePreferenceRank(const nsAString& aAcceptLangs) const;
-
-  /**
-   * Check whether the conditional processing attributes other than
-   * systemLanguage "return true" if they apply to and are specified
-   * on the given element. Returns true if this element should be
-   * rendered, false if it should not.
+   * Find the active switch child using BCP 47 rules.
    */
-  bool PassesConditionalProcessingTestsIgnoringSystemLanguage() const;
+  static nsIContent* FindActiveSwitchChild(
+      const dom::SVGSwitchElement* aSwitch);
 
   /**
    * Check whether the conditional processing attributes requiredExtensions
@@ -72,16 +58,6 @@ class SVGTests : public nsISupports {
   bool PassesConditionalProcessingTests() const;
 
   /**
-   * Check whether the conditional processing attributes requiredExtensions
-   * and systemLanguage both "return true" if they apply to
-   * and are specified on the given element. Returns true if this element
-   * should be rendered, false if it should not.
-   *
-   * @param aAcceptLangs The value of the intl.accept_languages preference
-   */
-  bool PassesConditionalProcessingTests(const nsAString& aAcceptLangs) const;
-
-  /**
    * Returns true if the attribute is one of the conditional processing
    * attributes.
    */
@@ -117,9 +93,17 @@ class SVGTests : public nsISupports {
   virtual ~SVGTests() = default;
 
  private:
+  /**
+   * Check whether the extensions processing attribute applies to and is
+   * specified on the given element. Returns true if this element should be
+   * rendered, false if it should not.
+   */
+  bool PassesRequiredExtensionsTests() const;
+
   enum { EXTENSIONS, LANGUAGE };
   SVGStringList mStringListAttributes[2];
   static nsStaticAtom* const sStringListNames[2];
+  mutable Maybe<bool> mPassesConditionalProcessingTests = Some(true);
 };
 
 NS_DEFINE_STATIC_IID_ACCESSOR(SVGTests, MOZILLA_DOMSVGTESTS_IID)
diff --git a/dom/svg/test/test_switch.xhtml b/dom/svg/test/test_switch.xhtml
index d1fa546e26..a589a934c1 100644
--- a/dom/svg/test/test_switch.xhtml
+++ b/dom/svg/test/test_switch.xhtml
@@ -22,17 +22,6 @@ SimpleTest.waitForExplicitFinish();
 
 var test = 1;
 
-function checkBounds(element, x, y, w, h) {
-  var bbox = element.getBBox();
-  var name = element.nodeName;
-
-  is(bbox.x, x, test + " " + name + ".getBBox().x");
-  is(bbox.y, y, test + " " + name + ".getBBox().y");
-  is(bbox.width, w, test + " " + name + ".getBBox().width");
-  is(bbox.height, h, test + " " + name + ".getBBox().height");
-  ++test;
-}
-
 function checkWidth(element, w) {
   var bbox = element.getBBox();
   var name = element.nodeName;
@@ -41,55 +30,65 @@ function checkWidth(element, w) {
   ++test;
 }
 
-function run() {
-  // Set accept_languages to something we know
-  SpecialPowers.pushPrefEnv({"set": [["intl.accept_languages", "en-gb,en,it"]]}, run1);
-}
-
-function run1() {
+async function run() {
   try {
-    var doc = $("svg").contentDocument;
-    var s = doc.getElementById("s");
-    var first = doc.getElementById("first");
-    var second = doc.getElementById("second");
-    var third = doc.getElementById("third");
-
-    first.setAttribute("systemLanguage", "fr");
-
-    /* test for an exact match */
-    second.setAttribute("systemLanguage", "en-gb");
-    checkWidth(s, 50);
-
-    /* test for a close match i.e. the same language prefix */
-    second.setAttribute("systemLanguage", "en-us");
-    checkWidth(s, 50);
-
-    /* test that we pick the best match */
-    second.setAttribute("systemLanguage", "it");
-    checkWidth(s, 50);
-
-    /* test that we use the default if nothing matches */
-    second.setAttribute("systemLanguage", "fr");
-    checkWidth(s, 80);
-
-    /* test we still ignore non-matches */
-    second.removeAttribute("systemLanguage");
-    third.setAttribute("systemLanguage", "fr");
-    checkWidth(s, 50);
-
-    /* check what happens if nothing matches */
-    second.setAttribute("systemLanguage", "fr");
-    checkWidth(s, 0);
-
-    /* test that we pick the best match */
-    first.setAttribute("systemLanguage", "en");
-    second.setAttribute("systemLanguage", "en-gb");
-    checkWidth(s, 50);
+    // Set accept_languages to something we know
+    await SpecialPowers.pushPrefEnv({"set": [["intl.accept_languages", "en-gb,en,it"]]}, run1);
   } finally {
     SimpleTest.finish();
   }
 }
 
+function run1() {
+  let doc = $("svg").contentDocument;
+  let s = doc.getElementById("s");
+  let first = doc.getElementById("first");
+  let second = doc.getElementById("second");
+  let third = doc.getElementById("third");
+
+  first.setAttribute("systemLanguage", "fr");
+
+  /* test for an exact match */
+  second.setAttribute("systemLanguage", "en-gb");
+  checkWidth(s, 50);
+
+  /* test for a close match i.e. the same language prefix */
+  second.setAttribute("systemLanguage", "en");
+  checkWidth(s, 50);
+
+  /* test for a close match regardless of case */
+  second.setAttribute("systemLanguage", "eN");
+  checkWidth(s, 50);
+
+  /* test that different regions don't match */
+  second.setAttribute("systemLanguage", "en-us");
+  checkWidth(s, 80);
+
+  /* test that we pick the best match */
+  second.setAttribute("systemLanguage", "it");
+  checkWidth(s, 50);
+
+  /* test that we use the default if nothing matches */
+  second.setAttribute("systemLanguage", "fr");
+  checkWidth(s, 80);
+
+  /* test we still ignore non-matches */
+  second.removeAttribute("systemLanguage");
+  third.setAttribute("systemLanguage", "fr");
+  checkWidth(s, 50);
+
+  /* check what happens if nothing matches */
+  second.setAttribute("systemLanguage", "fr");
+  third.setAttribute("systemLanguage", "fr");
+  checkWidth(s, 0);
+
+  /* test that we pick the best match */
+  first.setAttribute("systemLanguage", "en");
+  second.setAttribute("systemLanguage", "en-gb");
+  third.removeAttribute("systemLanguage");
+  checkWidth(s, 50);
+}
+
 window.addEventListener("load", run);
 
 ]]>
diff --git a/dom/svg/test/test_tabindex.html b/dom/svg/test/test_tabindex.html
index 65315420bc..3d29d1070b 100644
--- a/dom/svg/test/test_tabindex.html
+++ b/dom/svg/test/test_tabindex.html
@@ -37,7 +37,6 @@ function main() {
   var t = document.getElementById("t");
   var l1 = document.getElementById("l1");
   var l2 = document.getElementById("l2");
-  const isMac = ("nsILocalFileMac" in SpecialPowers.Ci);
 
   try {
     // Step 1: Checking by assigning tabIndex
@@ -74,20 +73,10 @@ function main() {
     is(document.activeElement.tabIndex, 3, "The active element tabindex is 3");
 
     synthesizeKey("KEY_Tab");
-    // On Mac, SVG link elements should not be focused.
-    if (isMac) {
-      is(document.activeElement.tabIndex, 6, "The active element tabindex is 6");
-    } else {
-      is(document.activeElement.tabIndex, 4, "The active element tabindex is 4");
-    }
+    is(document.activeElement.tabIndex, 4, "The active element tabindex is 4");
 
     synthesizeKey("KEY_Tab");
-    // On Mac, SVG link elements should not be focused.
-    if (isMac) {
-      is(document.activeElement.tabIndex, 7, "The active element tabindex is 7");
-    } else {
-      is(document.activeElement.tabIndex, 5, "The active element tabindex is 5");
-    }
+    is(document.activeElement.tabIndex, 5, "The active element tabindex is 5");
   } catch (e) {
     ok(false, "Got unexpected exception" + e);
   }