diff --git a/dom/chrome-webidl/InspectorUtils.webidl b/dom/chrome-webidl/InspectorUtils.webidl
index 8ae374e2efd7..c1a96f6a9ff0 100644
--- a/dom/chrome-webidl/InspectorUtils.webidl
+++ b/dom/chrome-webidl/InspectorUtils.webidl
@@ -11,7 +11,8 @@
  */
 [ChromeOnly]
 namespace InspectorUtils {
-  sequence<StyleSheet> getAllStyleSheets(Document document);
+  // documentOnly tells whether user and UA sheets should get included.
+  sequence<StyleSheet> getAllStyleSheets(Document document, optional boolean documentOnly = false);
   sequence<CSSRule> getCSSStyleRules(
     Element element,
     [TreatNullAs=EmptyString] optional DOMString pseudo = "");
diff --git a/layout/inspector/InspectorUtils.cpp b/layout/inspector/InspectorUtils.cpp
index e94530e8e8de..3c23e19ca369 100644
--- a/layout/inspector/InspectorUtils.cpp
+++ b/layout/inspector/InspectorUtils.cpp
@@ -61,6 +61,7 @@ namespace dom {
 /* static */ void
 InspectorUtils::GetAllStyleSheets(GlobalObject& aGlobalObject,
                                   nsIDocument& aDocument,
+                                  bool aDocumentOnly,
                                   nsTArray<RefPtr<StyleSheet>>& aResult)
 {
   // Get the agent, then user and finally xbl sheets in the style set.
@@ -68,19 +69,24 @@ InspectorUtils::GetAllStyleSheets(GlobalObject& aGlobalObject,
 
   if (presShell) {
     ServoStyleSet* styleSet = presShell->StyleSet();
-    SheetType sheetType = SheetType::Agent;
-    for (int32_t i = 0; i < styleSet->SheetCount(sheetType); i++) {
-      aResult.AppendElement(styleSet->StyleSheetAt(sheetType, i));
-    }
-    sheetType = SheetType::User;
-    for (int32_t i = 0; i < styleSet->SheetCount(sheetType); i++) {
-      aResult.AppendElement(styleSet->StyleSheetAt(sheetType, i));
+
+    if (!aDocumentOnly) {
+      SheetType sheetType = SheetType::Agent;
+      for (int32_t i = 0; i < styleSet->SheetCount(sheetType); i++) {
+        aResult.AppendElement(styleSet->StyleSheetAt(sheetType, i));
+      }
+      sheetType = SheetType::User;
+      for (int32_t i = 0; i < styleSet->SheetCount(sheetType); i++) {
+        aResult.AppendElement(styleSet->StyleSheetAt(sheetType, i));
+      }
     }
 
     AutoTArray<StyleSheet*, 32> xblSheetArray;
-    styleSet->AppendAllXBLStyleSheets(xblSheetArray);
+    styleSet->AppendAllNonDocumentAuthorSheets(xblSheetArray);
 
     // The XBL stylesheet array will quite often be full of duplicates. Cope:
+    //
+    // FIXME(emilio, bug 1454467): I think this is not true since bug 1452525.
     nsTHashtable<nsPtrHashKey<StyleSheet>> sheetSet;
     for (StyleSheet* sheet : xblSheetArray) {
       if (!sheetSet.Contains(sheet)) {
@@ -1048,16 +1054,8 @@ InspectorUtils::ParseStyleSheet(GlobalObject& aGlobalObject,
                                 ErrorResult& aRv)
 {
 
-  RefPtr<ServoStyleSheet> servoSheet = do_QueryObject(&aSheet);
-  if (servoSheet) {
-    nsresult rv = servoSheet->ReparseSheet(aInput);
-    if (NS_FAILED(rv)) {
-      aRv.Throw(rv);
-    }
-    return;
-  }
-
-  aRv.Throw(NS_ERROR_INVALID_POINTER);
+  RefPtr<ServoStyleSheet> servoSheet = aSheet.AsServo();
+  aRv = servoSheet->ReparseSheet(aInput);
 }
 
 void
diff --git a/layout/inspector/InspectorUtils.h b/layout/inspector/InspectorUtils.h
index d4968cec6141..8efa267b8f42 100644
--- a/layout/inspector/InspectorUtils.h
+++ b/layout/inspector/InspectorUtils.h
@@ -37,6 +37,7 @@ class InspectorUtils
 public:
   static void GetAllStyleSheets(GlobalObject& aGlobal,
                                 nsIDocument& aDocument,
+                                bool aDocumentOnly,
                                 nsTArray<RefPtr<StyleSheet>>& aResult);
   static void GetCSSStyleRules(GlobalObject& aGlobal,
                                Element& aElement,
diff --git a/layout/style/ErrorReporter.cpp b/layout/style/ErrorReporter.cpp
index defbbdc8abd6..a3ae41a24fc1 100644
--- a/layout/style/ErrorReporter.cpp
+++ b/layout/style/ErrorReporter.cpp
@@ -146,6 +146,7 @@ ErrorReporter::ErrorReporter(const StyleSheet* aSheet,
 
 ErrorReporter::~ErrorReporter()
 {
+  MOZ_ASSERT(NS_IsMainThread());
   // Schedule deferred cleanup for cached data. We want to strike a
   // balance between performance and memory usage, so we only allow
   // short-term caching.
diff --git a/layout/style/ServoStyleSet.cpp b/layout/style/ServoStyleSet.cpp
index 76951ae58dc2..c52f2e7054e9 100644
--- a/layout/style/ServoStyleSet.cpp
+++ b/layout/style/ServoStyleSet.cpp
@@ -869,10 +869,15 @@ ServoStyleSet::StyleSheetAt(SheetType aType, int32_t aIndex) const
 }
 
 void
-ServoStyleSet::AppendAllXBLStyleSheets(nsTArray<StyleSheet*>& aArray) const
+ServoStyleSet::AppendAllNonDocumentAuthorSheets(nsTArray<StyleSheet*>& aArray) const
 {
   if (mDocument) {
     mDocument->BindingManager()->AppendAllSheets(aArray);
+    EnumerateShadowRoots(*mDocument, [&](ShadowRoot& aShadowRoot) {
+      for (auto index : IntegerRange(aShadowRoot.SheetCount())) {
+        aArray.AppendElement(aShadowRoot.SheetAt(index));
+      }
+    });
   }
 }
 
diff --git a/layout/style/ServoStyleSet.h b/layout/style/ServoStyleSet.h
index 178e70f6f4dc..94ae168c5115 100644
--- a/layout/style/ServoStyleSet.h
+++ b/layout/style/ServoStyleSet.h
@@ -244,7 +244,7 @@ public:
   int32_t SheetCount(SheetType aType) const;
   ServoStyleSheet* StyleSheetAt(SheetType aType, int32_t aIndex) const;
 
-  void AppendAllXBLStyleSheets(nsTArray<StyleSheet*>& aArray) const;
+  void AppendAllNonDocumentAuthorSheets(nsTArray<StyleSheet*>& aArray) const;
 
   template<typename Func>
   void EnumerateStyleSheetArrays(Func aCallback) const {