--- a/dom/base/nsDOMWindowUtils.cpp
+++ b/dom/base/nsDOMWindowUtils.cpp
@@ -4499,16 +4499,34 @@ nsDOMWindowUtils::EnsureDirtyRootFrame()
 NS_IMETHODIMP
 nsDOMWindowUtils::GetIsStyledByServo(bool* aStyledByServo)
 {
   nsIDocument* doc = GetDocument();
   *aStyledByServo = doc && doc->IsStyledByServo();
   return NS_OK;
 }
 
+NS_IMETHODIMP
+nsDOMWindowUtils::AddToStyloBlocklist(const nsACString& aBlockedDomain)
+{
+#ifdef MOZ_STYLO
+  nsLayoutUtils::AddToStyloBlocklist(aBlockedDomain);
+#endif
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsDOMWindowUtils::RemoveFromStyloBlocklist(const nsACString& aBlockedDomain)
+{
+#ifdef MOZ_STYLO
+  nsLayoutUtils::RemoveFromStyloBlocklist(aBlockedDomain);
+#endif
+  return NS_OK;
+}
+
 NS_INTERFACE_MAP_BEGIN(nsTranslationNodeList)
   NS_INTERFACE_MAP_ENTRY(nsISupports)
   NS_INTERFACE_MAP_ENTRY(nsITranslationNodeList)
 NS_INTERFACE_MAP_END
 
 NS_IMPL_ADDREF(nsTranslationNodeList)
 NS_IMPL_RELEASE(nsTranslationNodeList)
 

--- a/dom/interfaces/base/nsIDOMWindowUtils.idl
+++ b/dom/interfaces/base/nsIDOMWindowUtils.idl
@@ -2041,16 +2041,30 @@ interface nsIDOMWindowUtils : nsISupport
 
   /**
    * Whether the current document is styled by Servo's style engine.
    *
    * This calls nsIDocument::IsStyledByServo().
    */
   readonly attribute boolean isStyledByServo;
 
+  /**
+   * Add a domain to the existing stylo blocklist.
+   *
+   * This calls nsLayoutUtils::AddToStyloBlocklist().
+   */
+  void addToStyloBlocklist(in ACString aBlockedDomain);
+
+  /**
+   * Remove a domain from the existing stylo blocklist.
+   *
+   * This calls nsLayoutUtils::RemoveFromStyloBlocklist().
+   */
+  void removeFromStyloBlocklist(in ACString aBlockedDomain);
+
   // These consts are only for testing purposes.
   const long DEFAULT_MOUSE_POINTER_ID = 0;
   const long DEFAULT_PEN_POINTER_ID   = 1;
   const long DEFAULT_TOUCH_POINTER_ID = 2;
 
   // Match WidgetMouseEventBase::buttonType.
   const long MOUSE_BUTTON_LEFT_BUTTON   = 0;
   const long MOUSE_BUTTON_MIDDLE_BUTTON = 1;

--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -8056,16 +8056,42 @@ nsLayoutUtils::IsInStyloBlocklist(nsIPri
   NS_SUCCEEDED(tldService->GetBaseDomain(codebaseURI, 0, baseDomain));
   for (const nsCString& domains : *sStyloBlocklist) {
     if (baseDomain.Equals(domains)) {
       return true;
     }
   }
   return false;
 }
+
+/* static */
+void
+nsLayoutUtils::AddToStyloBlocklist(const nsACString& aBlockedDomain)
+{
+  if (!sStyloBlocklist) {
+    sStyloBlocklist = new nsTArray<nsCString>;
+  }
+  sStyloBlocklist->AppendElement(aBlockedDomain);
+}
+
+/* static */
+void
+nsLayoutUtils::RemoveFromStyloBlocklist(const nsACString& aBlockedDomain)
+{
+  if (!sStyloBlocklist) {
+    return;
+  }
+
+  sStyloBlocklist->RemoveElement(aBlockedDomain);
+
+  if (sStyloBlocklist->IsEmpty()) {
+    delete sStyloBlocklist;
+    sStyloBlocklist = nullptr;
+  }
+}
 #endif
 
 /* static */
 void
 nsLayoutUtils::RegisterImageRequest(nsPresContext* aPresContext,
                                     imgIRequest* aRequest,
                                     bool* aRequestRegistered)
 {

--- a/layout/base/nsLayoutUtils.h
+++ b/layout/base/nsLayoutUtils.h
@@ -2562,16 +2562,30 @@ public:
   /**
    * Principal-based blocklist for stylo.
    * Check if aPrincipal is blocked by stylo's blocklist and should fallback to
    * use Gecko's style backend. Note that using a document's principal rather
    * than the document URI will let us piggy-back off the existing principal
    * relationships and symmetries.
    */
   static bool IsInStyloBlocklist(nsIPrincipal* aPrincipal);
+
+  /**
+   * Add aBlockedDomain to the existing stylo blocklist, i.e., sStyloBlocklist.
+   * This function is exposed to nsDOMWindowUtils and only for testing purpose.
+   * So, NEVER use this in any other cases.
+   */
+  static void AddToStyloBlocklist(const nsACString& aBlockedDomain);
+
+  /**
+   * Remove aBlockedDomain from the existing stylo blocklist, i.e., sStyloBlocklist.
+   * This function is exposed to nsDOMWindowUtils and only for testing purpose.
+   * So, NEVER use this in any other cases.
+   */
+  static void RemoveFromStyloBlocklist(const nsACString& aBlockedDomain);
 #endif
 
   /**
    * Register an imgIRequest object with a refresh driver.
    *
    * @param aPresContext The nsPresContext whose refresh driver we want to
    *        register with.
    * @param aRequest A pointer to the imgIRequest object which the client wants