diff --git a/dom/base/nsContentUtils.cpp b/dom/base/nsContentUtils.cpp
index 7cb03fdf6d28..90eebb0560d8 100644
--- a/dom/base/nsContentUtils.cpp
+++ b/dom/base/nsContentUtils.cpp
@@ -5091,7 +5091,8 @@ nsContentUtils::ParseFragmentHTML(const nsAString& aSourceBuffer,
   // If this is a chrome-privileged document, create a fragment first, and
   // sanitize it before insertion.
   RefPtr<DocumentFragment> fragment;
-  if (aSanitize != NeverSanitize && !aTargetNode->OwnerDoc()->AllowUnsafeHTML()) {
+  if (aSanitize != NeverSanitize &&
+      IsSystemPrincipal(aTargetNode->NodePrincipal())) {
     fragment = new DocumentFragment(aTargetNode->OwnerDoc()->NodeInfoManager());
     target = fragment;
   }
@@ -5198,7 +5199,8 @@ nsContentUtils::ParseFragmentXML(const nsAString& aSourceBuffer,
 
   // If this is a chrome-privileged document, sanitize the fragment before
   // returning.
-  if (aSanitize != NeverSanitize && !aDocument->AllowUnsafeHTML()) {
+  if (aSanitize != NeverSanitize &&
+      IsSystemPrincipal(aDocument->NodePrincipal())) {
     // Don't fire mutation events for nodes removed by the sanitizer.
     nsAutoScriptBlockerSuppressNodeRemoved scriptBlocker;
 
diff --git a/dom/base/nsDocument.cpp b/dom/base/nsDocument.cpp
index df9b08826707..33ec9c37051c 100644
--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -1434,7 +1434,6 @@ nsIDocument::nsIDocument()
     mEncodingMenuDisabled(false),
     mIsShadowDOMEnabled(false),
     mIsSVGGlyphsDocument(false),
-    mAllowUnsafeHTML(false),
     mInDestructor(false),
     mIsGoingAway(false),
     mInXBLUpdate(false),
@@ -5862,13 +5861,6 @@ nsIDocument::CreateAttributeNS(const nsAString& aNamespaceURI,
   return attribute.forget();
 }
 
-bool
-nsIDocument::AllowUnsafeHTML() const
-{
-  return (!nsContentUtils::IsSystemPrincipal(NodePrincipal()) ||
-          mAllowUnsafeHTML);
-}
-
 void
 nsIDocument::ResolveScheduledSVGPresAttrs()
 {
diff --git a/dom/base/nsIDocument.h b/dom/base/nsIDocument.h
index 4a20e844c353..a8b94c0ebac2 100644
--- a/dom/base/nsIDocument.h
+++ b/dom/base/nsIDocument.h
@@ -3211,8 +3211,6 @@ public:
     CreateAttributeNS(const nsAString& aNamespaceURI,
                       const nsAString& aQualifiedName,
                       mozilla::ErrorResult& rv);
-  void SetAllowUnsafeHTML(bool aAllow) { mAllowUnsafeHTML = aAllow; }
-  bool AllowUnsafeHTML() const;
   void GetInputEncoding(nsAString& aInputEncoding) const;
   already_AddRefed<mozilla::dom::Location> GetLocation() const;
   void GetReferrer(nsAString& aReferrer) const;
@@ -4044,10 +4042,6 @@ protected:
   // True if this document is for an SVG-in-OpenType font.
   bool mIsSVGGlyphsDocument : 1;
 
-  // True if unsafe HTML fragments should be allowed in chrome-privileged
-  // documents.
-  bool mAllowUnsafeHTML : 1;
-
   // True if the document is being destroyed.
   bool mInDestructor: 1;
 
diff --git a/dom/webidl/Document.webidl b/dom/webidl/Document.webidl
index 29520f483fe5..fff315487b84 100644
--- a/dom/webidl/Document.webidl
+++ b/dom/webidl/Document.webidl
@@ -106,11 +106,6 @@ interface Document : Node {
   Attr createAttribute(DOMString name);
   [NewObject, Throws]
   Attr createAttributeNS(DOMString? namespace, DOMString name);
-
-  // Allows setting innerHTML without automatic sanitization.
-  // Do not use this.
-  [ChromeOnly]
-  attribute boolean allowUnsafeHTML;
 };
 
 // https://html.spec.whatwg.org/multipage/dom.html#the-document-object