--- a/caps/BasePrincipal.cpp
+++ b/caps/BasePrincipal.cpp
@@ -254,34 +254,9 @@ BasePrincipal::CreateCodebasePrincipal(n
 
   // Mint a codebase principal.
   nsRefPtr<nsPrincipal> codebase = new nsPrincipal();
   rv = codebase->Init(aURI, aAttrs);
   NS_ENSURE_SUCCESS(rv, nullptr);
   return codebase.forget();
 }
 
-/* static */ bool
-BasePrincipal::IsCodebasePrincipal(nsIPrincipal* aPrincipal)
-{
-  MOZ_ASSERT(aPrincipal);
-
-  bool isNullPrincipal = true;
-  nsresult rv = aPrincipal->GetIsNullPrincipal(&isNullPrincipal);
-  if (NS_WARN_IF(NS_FAILED(rv))) {
-    return false;
-  }
-
-  if (isNullPrincipal || nsContentUtils::IsSystemPrincipal(aPrincipal)) {
-    return false;
-  }
-
-  // No expanded principals.
-  nsCOMPtr<nsIExpandedPrincipal> expandedPrincipal =
-    do_QueryInterface(aPrincipal);
-  if (expandedPrincipal) {
-    return false;
-  }
-
-  return true;
-}
-
 } // namespace mozilla

--- a/caps/BasePrincipal.h
+++ b/caps/BasePrincipal.h
@@ -78,17 +78,17 @@ public:
   NS_IMETHOD GetCookieJar(nsACString& aCookieJar) final;
   NS_IMETHOD GetAppStatus(uint16_t* aAppStatus) final;
   NS_IMETHOD GetAppId(uint32_t* aAppStatus) final;
   NS_IMETHOD GetIsInBrowserElement(bool* aIsInBrowserElement) final;
   NS_IMETHOD GetUnknownAppId(bool* aUnknownAppId) final;
 
   virtual bool IsOnCSSUnprefixingWhitelist() override { return false; }
 
-  static bool IsCodebasePrincipal(nsIPrincipal* aPrincipal);
+  virtual bool IsCodebasePrincipal() const { return false; };
 
   static BasePrincipal* Cast(nsIPrincipal* aPrin) { return static_cast<BasePrincipal*>(aPrin); }
   static already_AddRefed<BasePrincipal> CreateCodebasePrincipal(nsIURI* aURI, OriginAttributes& aAttrs);
 
   const OriginAttributes& OriginAttributesRef() { return mOriginAttributes; }
   uint32_t AppId() const { return mOriginAttributes.mAppId; }
   bool IsInBrowserElement() const { return mOriginAttributes.mInBrowser; }
 

--- a/caps/nsPrincipal.h
+++ b/caps/nsPrincipal.h
@@ -24,16 +24,17 @@ public:
   NS_IMETHOD QueryInterface(REFNSIID aIID, void** aInstancePtr) override;
   NS_IMETHOD GetHashValue(uint32_t* aHashValue) override;
   NS_IMETHOD GetURI(nsIURI** aURI) override;
   NS_IMETHOD GetDomain(nsIURI** aDomain) override;
   NS_IMETHOD SetDomain(nsIURI* aDomain) override;
   NS_IMETHOD CheckMayLoad(nsIURI* uri, bool report, bool allowIfInheritsPrincipal) override;
   NS_IMETHOD GetBaseDomain(nsACString& aBaseDomain) override;
   virtual bool IsOnCSSUnprefixingWhitelist() override;
+  bool IsCodebasePrincipal() const override { return true; }
   nsresult GetOriginInternal(nsACString& aOrigin) override;
 
   nsPrincipal();
 
   // Init() must be called before the principal is in a usable state.
   nsresult Init(nsIURI* aCodebase, const mozilla::OriginAttributes& aOriginAttributes);
 
   virtual void GetScriptLocation(nsACString& aStr) override;

--- a/dom/workers/ServiceWorkerManager.cpp
+++ b/dom/workers/ServiceWorkerManager.cpp
@@ -224,17 +224,17 @@ namespace {
 nsresult
 PopulateRegistrationData(nsIPrincipal* aPrincipal,
                          const ServiceWorkerRegistrationInfo* aRegistration,
                          ServiceWorkerRegistrationData& aData)
 {
   MOZ_ASSERT(aPrincipal);
   MOZ_ASSERT(aRegistration);
 
-  if (NS_WARN_IF(!BasePrincipal::IsCodebasePrincipal(aPrincipal))) {
+  if (NS_WARN_IF(!BasePrincipal::Cast(aPrincipal)->IsCodebasePrincipal())) {
     return NS_ERROR_FAILURE;
   }
 
   nsresult rv = PrincipalToPrincipalInfo(aPrincipal, &aData.principal());
   if (NS_WARN_IF(NS_FAILED(rv))) {
     return rv;
   }
 
@@ -1586,17 +1586,17 @@ public:
     nsCOMPtr<nsIPrincipal> principal = doc->NodePrincipal();
     if (!principal) {
       mPromise->MaybeReject(NS_ERROR_UNEXPECTED);
       return NS_OK;
     }
 
     nsTArray<nsRefPtr<ServiceWorkerRegistrationMainThread>> array;
 
-    if (NS_WARN_IF(!BasePrincipal::IsCodebasePrincipal(principal))) {
+    if (NS_WARN_IF(!BasePrincipal::Cast(principal)->IsCodebasePrincipal())) {
       return NS_OK;
     }
 
     nsAutoCString scopeKey;
     nsresult rv = swm->PrincipalToScopeKey(principal, scopeKey);
     if (NS_WARN_IF(NS_FAILED(rv))) {
       return rv;
     }
@@ -2583,17 +2583,17 @@ ServiceWorkerManager::GetServiceWorkerRe
 }
 
 /* static */ nsresult
 ServiceWorkerManager::PrincipalToScopeKey(nsIPrincipal* aPrincipal,
                                           nsACString& aKey)
 {
   MOZ_ASSERT(aPrincipal);
 
-  if (NS_WARN_IF(!BasePrincipal::IsCodebasePrincipal(aPrincipal))) {
+  if (NS_WARN_IF(!BasePrincipal::Cast(aPrincipal)->IsCodebasePrincipal())) {
     return NS_ERROR_FAILURE;
   }
 
   nsresult rv = aPrincipal->GetOriginSuffix(aKey);
   if (NS_WARN_IF(NS_FAILED(rv))) {
     return rv;
   }