--- a/layout/base/nsPresContext.cpp
+++ b/layout/base/nsPresContext.cpp
@@ -1182,27 +1182,31 @@ nsPresContext::CompatibilityModeChanged(
     return;
   }
 
   nsIDocument* doc = mShell->GetDocument();
   if (!doc) {
     return;
   }
 
+  StyleSetHandle styleSet = mShell->StyleSet();
+  if (styleSet->IsServo()) {
+    styleSet->AsServo()->CompatibilityModeChanged();
+  }
+
   if (doc->IsSVGDocument()) {
     // SVG documents never load quirk.css.
     return;
   }
 
   bool needsQuirkSheet = CompatibilityMode() == eCompatibility_NavQuirks;
   if (mQuirkSheetAdded == needsQuirkSheet) {
     return;
   }
 
-  StyleSetHandle styleSet = mShell->StyleSet();
   auto cache = nsLayoutStylesheetCache::For(styleSet->BackendType());
   StyleSheet* sheet = cache->QuirkSheet();
 
   if (needsQuirkSheet) {
     // quirk.css needs to come after html.css; we just keep it at the end.
     DebugOnly<nsresult> rv =
       styleSet->AppendStyleSheet(SheetType::Agent, sheet);
     NS_WARNING_ASSERTION(NS_SUCCEEDED(rv), "failed to insert quirk.css");

--- a/layout/style/ServoBindingList.h
+++ b/layout/style/ServoBindingList.h
@@ -53,16 +53,18 @@ SERVO_BINDING_FUNC(Servo_StyleSheet_Size
 SERVO_BINDING_FUNC(Servo_StyleSet_Init, RawServoStyleSetOwned, RawGeckoPresContextOwned pres_context)
 SERVO_BINDING_FUNC(Servo_StyleSet_Clear, void,
                    RawServoStyleSetBorrowed set)
 SERVO_BINDING_FUNC(Servo_StyleSet_RebuildData, void,
                    RawServoStyleSetBorrowed set)
 SERVO_BINDING_FUNC(Servo_StyleSet_MediumFeaturesChanged, bool,
                    RawServoStyleSetBorrowed set)
 SERVO_BINDING_FUNC(Servo_StyleSet_Drop, void, RawServoStyleSetOwned set)
+SERVO_BINDING_FUNC(Servo_StyleSet_CompatModeChanged, void,
+                   RawServoStyleSetBorrowed raw_data)
 SERVO_BINDING_FUNC(Servo_StyleSet_AppendStyleSheet, void,
                    RawServoStyleSetBorrowed set,
                    RawServoStyleSheetBorrowed sheet,
                    uint64_t unique_id)
 SERVO_BINDING_FUNC(Servo_StyleSet_PrependStyleSheet, void,
                    RawServoStyleSetBorrowed set,
                    RawServoStyleSheetBorrowed sheet,
                    uint64_t unique_id)

--- a/layout/style/ServoStyleSet.cpp
+++ b/layout/style/ServoStyleSet.cpp
@@ -1118,16 +1118,22 @@ ServoStyleSet::RebuildData()
 void
 ServoStyleSet::ClearDataAndMarkDeviceDirty()
 {
   ClearNonInheritingStyleContexts();
   Servo_StyleSet_Clear(mRawSet.get());
   mStylistState |= StylistState::FullyDirty;
 }
 
+void
+ServoStyleSet::CompatibilityModeChanged()
+{
+  Servo_StyleSet_CompatModeChanged(mRawSet.get());
+}
+
 already_AddRefed<ServoComputedValues>
 ServoStyleSet::ResolveServoStyle(Element* aElement)
 {
   UpdateStylistIfNeeded();
   return Servo_ResolveStyle(aElement, mRawSet.get(),
                             mAllowResolveStaleStyles).Consume();
 }
 

--- a/layout/style/ServoStyleSet.h
+++ b/layout/style/ServoStyleSet.h
@@ -342,16 +342,21 @@ public:
   /**
    * Clears the style data, both style sheet data and cached non-inheriting
    * style contexts, and marks the stylist as needing an unconditional full
    * rebuild, including a device reset.
    */
   void ClearDataAndMarkDeviceDirty();
 
   /**
+   * Notifies the Servo stylesheet that the document's compatibility mode has changed.
+   */
+  void CompatibilityModeChanged();
+
+  /**
    * Resolve style for the given element, and return it as a
    * ServoComputedValues, not an nsStyleContext.
    */
   already_AddRefed<ServoComputedValues> ResolveServoStyle(dom::Element* aElement);
 
   bool GetKeyframesForName(const nsString& aName,
                            const nsTimingFunction& aTimingFunction,
                            const ServoComputedValues* aComputedValues,