diff --git a/dom/base/nsContentSink.cpp b/dom/base/nsContentSink.cpp
index 066ec84466..2040b1a70f 100644
--- a/dom/base/nsContentSink.cpp
+++ b/dom/base/nsContentSink.cpp
@@ -820,7 +820,8 @@ nsContentSink::ProcessStyleLink(nsIContent* aElement,
   // We don't support CORS for processing instructions
   bool isAlternate;
   bool isExplicitlyEnabled;
-  rv = mCSSLoader->LoadStyleLink(aElement, url, aTitle, aMedia, aAlternate,
+  rv = mCSSLoader->LoadStyleLink(aElement, url, nullptr /* triggeringPrincipal */, 
+                                 aTitle, aMedia, aAlternate,
                                  CORS_NONE, referrerPolicy,
                                  integrity, mRunsToCompletion ? nullptr : this,
                                  &isAlternate, &isExplicitlyEnabled);
diff --git a/dom/base/nsStyleLinkElement.cpp b/dom/base/nsStyleLinkElement.cpp
index 971af21b4c..2da27ca2f6 100644
--- a/dom/base/nsStyleLinkElement.cpp
+++ b/dom/base/nsStyleLinkElement.cpp
@@ -224,8 +224,7 @@ nsStyleLinkElement::UpdateStyleSheet(nsICSSLoaderObserver* aObserver,
 {
   if (aForceReload) {
     // We remove this stylesheet from the cache to load a new version.
-    nsCOMPtr<nsIContent> thisContent;
-    CallQueryInterface(this, getter_AddRefs(thisContent));
+    nsCOMPtr<nsIContent> thisContent = do_QueryInterface(this);
     nsCOMPtr<nsIDocument> doc = thisContent->IsInShadowTree() ?
       thisContent->OwnerDoc() : thisContent->GetUncomposedDoc();
     if (doc && doc->CSSLoader()->GetEnabled() &&
@@ -306,11 +305,10 @@ nsStyleLinkElement::DoUpdateStyleSheet(nsIDocument* aOldDocument,
 {
   *aWillNotify = false;
 
-  nsCOMPtr<nsIContent> thisContent;
-  CallQueryInterface(this, getter_AddRefs(thisContent));
+  nsCOMPtr<nsIContent> thisContent = do_QueryInterface(this);
 
   // All instances of nsStyleLinkElement should implement nsIContent.
-  NS_ENSURE_TRUE(thisContent, NS_ERROR_FAILURE);
+  MOZ_ASSERT(thisContent);
 
   if (thisContent->IsInAnonymousSubtree() &&
       thisContent->IsAnonymousContentInSVGUseSubtree()) {
@@ -362,7 +360,8 @@ nsStyleLinkElement::DoUpdateStyleSheet(nsIDocument* aOldDocument,
   }
 
   bool isInline;
-  nsCOMPtr<nsIURI> uri = GetStyleSheetURL(&isInline);
+  nsCOMPtr<nsIPrincipal> triggeringPrincipal;
+  nsCOMPtr<nsIURI> uri = GetStyleSheetURL(&isInline, getter_AddRefs(triggeringPrincipal));
 
   if (!aForceUpdate && mStyleSheet && !isInline && uri) {
     nsIURI* oldURI = mStyleSheet->GetSheetURI();
@@ -455,8 +454,8 @@ nsStyleLinkElement::DoUpdateStyleSheet(nsIDocument* aOldDocument,
     uri->Clone(getter_AddRefs(clonedURI));
     NS_ENSURE_TRUE(clonedURI, NS_ERROR_OUT_OF_MEMORY);
     rv = doc->CSSLoader()->
-      LoadStyleLink(thisContent, clonedURI, title, media, isAlternate,
-                    GetCORSMode(), referrerPolicy, integrity,
+      LoadStyleLink(thisContent, clonedURI, triggeringPrincipal, title, media,
+                    isAlternate, GetCORSMode(), referrerPolicy, integrity,
                     aObserver, &isAlternate, &isExplicitlyEnabled);
     if (NS_FAILED(rv)) {
       // Don't propagate LoadStyleLink() errors further than this, since some
@@ -486,8 +485,7 @@ nsStyleLinkElement::UpdateStyleSheetScopedness(bool aIsNowScoped)
 
   CSSStyleSheet* sheet = mStyleSheet->AsConcrete();
 
-  nsCOMPtr<nsIContent> thisContent;
-  CallQueryInterface(this, getter_AddRefs(thisContent));
+  nsCOMPtr<nsIContent> thisContent = do_QueryInterface(this);
 
   Element* oldScopeElement = sheet->GetScopeElement();
   Element* newScopeElement = aIsNowScoped ?
diff --git a/dom/base/nsStyleLinkElement.h b/dom/base/nsStyleLinkElement.h
index a76cd8a6b2..b7d57ca3d1 100644
--- a/dom/base/nsStyleLinkElement.h
+++ b/dom/base/nsStyleLinkElement.h
@@ -95,7 +95,7 @@ protected:
 
   void UpdateStyleSheetScopedness(bool aIsNowScoped);
 
-  virtual already_AddRefed<nsIURI> GetStyleSheetURL(bool* aIsInline) = 0;
+  virtual already_AddRefed<nsIURI> GetStyleSheetURL(bool* aIsInline, nsIPrincipal** aTriggeringPrincipal) = 0;
   virtual void GetStyleSheetInfo(nsAString& aTitle,
                                  nsAString& aType,
                                  nsAString& aMedia,
@@ -140,6 +140,7 @@ private:
 
   RefPtr<mozilla::StyleSheet> mStyleSheet;
 protected:
+  nsCOMPtr<nsIPrincipal> mTriggeringPrincipal;
   bool mDontLoadStyle;
   bool mUpdatesEnabled;
   uint32_t mLineNumber;
diff --git a/dom/html/HTMLLinkElement.cpp b/dom/html/HTMLLinkElement.cpp
index 7b6379ae3f..e4426f0c21 100644
--- a/dom/html/HTMLLinkElement.cpp
+++ b/dom/html/HTMLLinkElement.cpp
@@ -374,6 +374,12 @@ HTMLLinkElement::AfterSetAttr(int32_t aNameSpaceID, nsIAtom* aName,
     }
   }
 
+  if (aNameSpaceID == kNameSpaceID_None && aName == nsGkAtoms::href) {
+    mTriggeringPrincipal = nsContentUtils::GetAttrTriggeringPrincipal(
+        this, aValue ? aValue->GetStringValue() : EmptyString(),
+        aSubjectPrincipal);
+  }
+
   if (aValue) {
     if (aNameSpaceID == kNameSpaceID_None &&
         (aName == nsGkAtoms::href ||
@@ -520,14 +526,20 @@ HTMLLinkElement::GetHrefURI() const
 }
 
 already_AddRefed<nsIURI>
-HTMLLinkElement::GetStyleSheetURL(bool* aIsInline)
+HTMLLinkElement::GetStyleSheetURL(bool* aIsInline, nsIPrincipal** aTriggeringPrincipal)
 {
   *aIsInline = false;
+  *aTriggeringPrincipal = nullptr;
+
   nsAutoString href;
   GetAttr(kNameSpaceID_None, nsGkAtoms::href, href);
   if (href.IsEmpty()) {
     return nullptr;
   }
+
+  nsCOMPtr<nsIPrincipal> prin = mTriggeringPrincipal;
+  prin.forget(aTriggeringPrincipal);
+
   nsCOMPtr<nsIURI> uri = Link::GetURI();
   return uri.forget();
 }
diff --git a/dom/html/HTMLLinkElement.h b/dom/html/HTMLLinkElement.h
index 7eb6b78e18..2c4af10c7f 100644
--- a/dom/html/HTMLLinkElement.h
+++ b/dom/html/HTMLLinkElement.h
@@ -88,10 +88,14 @@ public:
   // WebIDL
   bool Disabled() const;
   void SetDisabled(bool aDisabled, ErrorResult& aRv);
-  // XPCOM GetHref is fine.
-  void SetHref(const nsAString& aHref, ErrorResult& aRv)
+
+  void GetHref(nsString& aValue, nsIPrincipal&)
   {
-    SetHTMLAttr(nsGkAtoms::href, aHref, aRv);
+    GetHref(aValue);
+  }
+  void SetHref(const nsAString& aHref, nsIPrincipal& aTriggeringPrincipal, ErrorResult& aRv)
+  {
+    SetHTMLAttr(nsGkAtoms::href, aHref, aTriggeringPrincipal, aRv);
   }
   void GetCrossOrigin(nsAString& aResult)
   {
@@ -189,7 +193,7 @@ protected:
   virtual ~HTMLLinkElement();
 
   // nsStyleLinkElement
-  virtual already_AddRefed<nsIURI> GetStyleSheetURL(bool* aIsInline) override;
+  virtual already_AddRefed<nsIURI> GetStyleSheetURL(bool* aIsInline, nsIPrincipal** aTriggeringPrincipal) override;
   virtual void GetStyleSheetInfo(nsAString& aTitle,
                                  nsAString& aType,
                                  nsAString& aMedia,
diff --git a/dom/html/HTMLStyleElement.cpp b/dom/html/HTMLStyleElement.cpp
index 4cc4477a55..f9e544ac30 100644
--- a/dom/html/HTMLStyleElement.cpp
+++ b/dom/html/HTMLStyleElement.cpp
@@ -214,9 +214,10 @@ HTMLStyleElement::SetInnerHTML(const nsAString& aInnerHTML,
 }
 
 already_AddRefed<nsIURI>
-HTMLStyleElement::GetStyleSheetURL(bool* aIsInline)
+HTMLStyleElement::GetStyleSheetURL(bool* aIsInline, nsIPrincipal** aTriggeringPrincipal)
 {
   *aIsInline = true;
+  *aTriggeringPrincipal = nullptr;
   return nullptr;
 }
 
diff --git a/dom/html/HTMLStyleElement.h b/dom/html/HTMLStyleElement.h
index fe93b01d73..9bbf1da19f 100644
--- a/dom/html/HTMLStyleElement.h
+++ b/dom/html/HTMLStyleElement.h
@@ -91,7 +91,7 @@ public:
 protected:
   virtual ~HTMLStyleElement();
 
-  already_AddRefed<nsIURI> GetStyleSheetURL(bool* aIsInline) override;
+  already_AddRefed<nsIURI> GetStyleSheetURL(bool* aIsInline, nsIPrincipal** aTriggeringPrincipal) override;
   void GetStyleSheetInfo(nsAString& aTitle,
                          nsAString& aType,
                          nsAString& aMedia,
diff --git a/dom/svg/SVGStyleElement.cpp b/dom/svg/SVGStyleElement.cpp
index e91b498f2a..d5001f55a5 100644
--- a/dom/svg/SVGStyleElement.cpp
+++ b/dom/svg/SVGStyleElement.cpp
@@ -260,9 +260,10 @@ SVGStyleElement::SetTitle(const nsAString& aTitle, ErrorResult& rv)
 // nsStyleLinkElement methods
 
 already_AddRefed<nsIURI>
-SVGStyleElement::GetStyleSheetURL(bool* aIsInline)
+SVGStyleElement::GetStyleSheetURL(bool* aIsInline, nsIPrincipal** aTriggeringPrincipal)
 {
   *aIsInline = true;
+  *aTriggeringPrincipal = nullptr;
   return nullptr;
 }
 
diff --git a/dom/svg/SVGStyleElement.h b/dom/svg/SVGStyleElement.h
index 49d63520f4..8f87ef4c20 100644
--- a/dom/svg/SVGStyleElement.h
+++ b/dom/svg/SVGStyleElement.h
@@ -86,7 +86,7 @@ protected:
   }
 
   // nsStyleLinkElement overrides
-  already_AddRefed<nsIURI> GetStyleSheetURL(bool* aIsInline) override;
+  already_AddRefed<nsIURI> GetStyleSheetURL(bool* aIsInline, nsIPrincipal** aTriggeringPrincipal) override;
 
   void GetStyleSheetInfo(nsAString& aTitle,
                          nsAString& aType,
diff --git a/dom/webidl/HTMLLinkElement.webidl b/dom/webidl/HTMLLinkElement.webidl
index 11149ce6b6..da4827de19 100644
--- a/dom/webidl/HTMLLinkElement.webidl
+++ b/dom/webidl/HTMLLinkElement.webidl
@@ -16,7 +16,7 @@
 interface HTMLLinkElement : HTMLElement {
   [CEReactions, SetterThrows, Pure]
            attribute boolean disabled;
-  [CEReactions, SetterThrows, Pure]
+  [CEReactions, NeedsSubjectPrincipal, SetterThrows, Pure]
            attribute DOMString href;
   [CEReactions, SetterThrows, Pure]
            attribute DOMString? crossOrigin;
diff --git a/dom/xml/XMLStylesheetProcessingInstruction.cpp b/dom/xml/XMLStylesheetProcessingInstruction.cpp
index 52b87b2f9c..43609117e4 100644
--- a/dom/xml/XMLStylesheetProcessingInstruction.cpp
+++ b/dom/xml/XMLStylesheetProcessingInstruction.cpp
@@ -103,9 +103,10 @@ XMLStylesheetProcessingInstruction::OverrideBaseURI(nsIURI* aNewBaseURI)
 }
 
 already_AddRefed<nsIURI>
-XMLStylesheetProcessingInstruction::GetStyleSheetURL(bool* aIsInline)
+XMLStylesheetProcessingInstruction::GetStyleSheetURL(bool* aIsInline, nsIPrincipal** aTriggeringPrincipal)
 {
   *aIsInline = false;
+  *aTriggeringPrincipal = nullptr;
 
   nsAutoString href;
   if (!GetAttrValue(nsGkAtoms::href, href)) {
diff --git a/dom/xml/XMLStylesheetProcessingInstruction.h b/dom/xml/XMLStylesheetProcessingInstruction.h
index 3581d16bf1..b5b1fc4bf3 100644
--- a/dom/xml/XMLStylesheetProcessingInstruction.h
+++ b/dom/xml/XMLStylesheetProcessingInstruction.h
@@ -76,7 +76,7 @@ protected:
 
   nsCOMPtr<nsIURI> mOverriddenBaseURI;
 
-  already_AddRefed<nsIURI> GetStyleSheetURL(bool* aIsInline) override;
+  already_AddRefed<nsIURI> GetStyleSheetURL(bool* aIsInline, nsIPrincipal** aTriggeringPrincipal) override;
   void GetStyleSheetInfo(nsAString& aTitle,
                          nsAString& aType,
                          nsAString& aMedia,
diff --git a/layout/style/Loader.cpp b/layout/style/Loader.cpp
index 41ed9a1af5..581fe9622d 100644
--- a/layout/style/Loader.cpp
+++ b/layout/style/Loader.cpp
@@ -2015,6 +2015,7 @@ Loader::LoadInlineStyle(nsIContent* aElement,
 nsresult
 Loader::LoadStyleLink(nsIContent* aElement,
                       nsIURI* aURL,
+                      nsIPrincipal* aTriggeringPrincipal,
                       const nsAString& aTitle,
                       const nsAString& aMedia,
                       bool aHasAlternateRel,
@@ -2044,11 +2045,9 @@ Loader::LoadStyleLink(nsIContent* aElement,
   nsIPrincipal* loadingPrincipal = aElement ? aElement->NodePrincipal()
                                             : mDocument->NodePrincipal();
 
-  //SHOULD BE:
-  //nsIPrincipal* principal = aTriggeringPrincipal ? aTriggeringPrincipal
-  //                                               : loadingPrincipal;
-  nsIPrincipal* principal = loadingPrincipal;
-  
+  nsIPrincipal* principal = aTriggeringPrincipal ? aTriggeringPrincipal
+                                                 : loadingPrincipal;
+
   nsISupports* context = aElement;
   if (!context) {
     context = mDocument;
diff --git a/layout/style/Loader.h b/layout/style/Loader.h
index 830099b3ce..23cf2d54da 100644
--- a/layout/style/Loader.h
+++ b/layout/style/Loader.h
@@ -254,6 +254,9 @@ public:
    *
    * @param aElement the element linking to the the stylesheet.  May be null.
    * @param aURL the URL of the sheet.
+   * @param aTriggeringPrincipal the triggering principal for the load. May be
+   *        null, in which case the NodePrincipal() of the element (or
+   *        document if aElement is null) should be used.
    * @param aTitle the title of the sheet.
    * @param aMedia the media string for the sheet.
    * @param aHasAlternateRel whether the rel for this link included
@@ -269,6 +272,7 @@ public:
    */
   nsresult LoadStyleLink(nsIContent* aElement,
                          nsIURI* aURL,
+                         nsIPrincipal* aTriggeringPrincipal,
                          const nsAString& aTitle,
                          const nsAString& aMedia,
                          bool aHasAlternateRel,