diff --git a/caps/idl/nsIPrincipal.idl b/caps/idl/nsIPrincipal.idl
index 7117b87425fa..2770cd2abc53 100644
--- a/caps/idl/nsIPrincipal.idl
+++ b/caps/idl/nsIPrincipal.idl
@@ -20,7 +20,7 @@ interface nsIContentSecurityPolicy;
 [ptr] native JSPrincipals(JSPrincipals);
 [ptr] native PrincipalArray(nsTArray<nsCOMPtr<nsIPrincipal> >);
 
-[scriptable, builtinclass, uuid(f09d8a53-a6c8-4f68-b329-9a76a709d24e)]
+[scriptable, builtinclass, uuid(0416bfa5-c94b-485c-81a7-e48305c60289)]
 interface nsIPrincipal : nsISerializable
 {
     /**
@@ -35,6 +35,11 @@ interface nsIPrincipal : nsISerializable
      */
     boolean equalsIgnoringDomain(in nsIPrincipal other);
 
+    /**
+     * An alias for equals() (for now).
+     */
+    boolean equalsConsideringDomain(in nsIPrincipal other);
+
     %{C++
     inline bool Equals(nsIPrincipal* aOther) {
       bool equal = false;
@@ -45,6 +50,11 @@ interface nsIPrincipal : nsISerializable
       bool equal = false;
       return NS_SUCCEEDED(EqualsIgnoringDomain(aOther, &equal)) && equal;
     }
+
+    inline bool EqualsConsideringDomain(nsIPrincipal* aOther) {
+      bool equal = false;
+      return NS_SUCCEEDED(EqualsConsideringDomain(aOther, &equal)) && equal;
+    }
     %}
 
     /**
@@ -96,6 +106,11 @@ interface nsIPrincipal : nsISerializable
      */
     boolean subsumesIgnoringDomain(in nsIPrincipal other);
 
+    /**
+     * An alias for subsumes() (for now);
+     */
+    boolean subsumesConsideringDomain(in nsIPrincipal other);
+
     %{C++
     inline bool Subsumes(nsIPrincipal* aOther) {
       bool subsumes = false;
@@ -106,6 +121,11 @@ interface nsIPrincipal : nsISerializable
       bool subsumes = false;
       return NS_SUCCEEDED(SubsumesIgnoringDomain(aOther, &subsumes)) && subsumes;
     }
+
+    inline bool SubsumesConsideringDomain(nsIPrincipal* aOther) {
+      bool subsumes = false;
+      return NS_SUCCEEDED(SubsumesConsideringDomain(aOther, &subsumes)) && subsumes;
+    }
     %}
 
     /**
diff --git a/caps/include/nsPrincipal.h b/caps/include/nsPrincipal.h
index b0e15683ed05..f677c2004173 100644
--- a/caps/include/nsPrincipal.h
+++ b/caps/include/nsPrincipal.h
@@ -52,6 +52,7 @@ public:
   NS_DECL_NSISERIALIZABLE
   NS_IMETHOD Equals(nsIPrincipal* other, bool* _retval);
   NS_IMETHOD EqualsIgnoringDomain(nsIPrincipal* other, bool* _retval);
+  NS_IMETHOD EqualsConsideringDomain(nsIPrincipal* other, bool* _retval);
   NS_IMETHOD GetHashValue(uint32_t* aHashValue);
   NS_IMETHOD GetURI(nsIURI** aURI);
   NS_IMETHOD GetDomain(nsIURI** aDomain);
@@ -59,6 +60,7 @@ public:
   NS_IMETHOD GetOrigin(char** aOrigin);
   NS_IMETHOD Subsumes(nsIPrincipal* other, bool* _retval);
   NS_IMETHOD SubsumesIgnoringDomain(nsIPrincipal* other, bool* _retval);
+  NS_IMETHOD SubsumesConsideringDomain(nsIPrincipal* other, bool* _retval);
   NS_IMETHOD CheckMayLoad(nsIURI* uri, bool report, bool allowIfInheritsPrincipal);
   NS_IMETHOD GetJarPrefix(nsACString& aJarPrefix);
   NS_IMETHOD GetAppStatus(uint16_t* aAppStatus);
@@ -135,6 +137,7 @@ public:
   NS_DECL_NSISERIALIZABLE
   NS_IMETHOD Equals(nsIPrincipal* other, bool* _retval);
   NS_IMETHOD EqualsIgnoringDomain(nsIPrincipal* other, bool* _retval);
+  NS_IMETHOD EqualsConsideringDomain(nsIPrincipal* other, bool* _retval);
   NS_IMETHOD GetHashValue(uint32_t* aHashValue);
   NS_IMETHOD GetURI(nsIURI** aURI);
   NS_IMETHOD GetDomain(nsIURI** aDomain);
@@ -142,6 +145,7 @@ public:
   NS_IMETHOD GetOrigin(char** aOrigin);
   NS_IMETHOD Subsumes(nsIPrincipal* other, bool* _retval);
   NS_IMETHOD SubsumesIgnoringDomain(nsIPrincipal* other, bool* _retval);
+  NS_IMETHOD SubsumesConsideringDomain(nsIPrincipal* other, bool* _retval);
   NS_IMETHOD CheckMayLoad(nsIURI* uri, bool report, bool allowIfInheritsPrincipal);
   NS_IMETHOD GetJarPrefix(nsACString& aJarPrefix);
   NS_IMETHOD GetAppStatus(uint16_t* aAppStatus);
diff --git a/caps/src/nsNullPrincipal.cpp b/caps/src/nsNullPrincipal.cpp
index 8fc74e16e6ca..f1f290fc9c87 100644
--- a/caps/src/nsNullPrincipal.cpp
+++ b/caps/src/nsNullPrincipal.cpp
@@ -139,6 +139,12 @@ nsNullPrincipal::EqualsIgnoringDomain(nsIPrincipal *aOther, bool *aResult)
   return Equals(aOther, aResult);
 }
 
+NS_IMETHODIMP
+nsNullPrincipal::EqualsConsideringDomain(nsIPrincipal *aOther, bool *aResult)
+{
+  return Equals(aOther, aResult);
+}
+
 NS_IMETHODIMP
 nsNullPrincipal::GetHashValue(uint32_t *aResult)
 {
@@ -216,6 +222,12 @@ nsNullPrincipal::SubsumesIgnoringDomain(nsIPrincipal *aOther, bool *aResult)
   return Subsumes(aOther, aResult);
 }
 
+NS_IMETHODIMP
+nsNullPrincipal::SubsumesConsideringDomain(nsIPrincipal *aOther, bool *aResult)
+{
+  return Subsumes(aOther, aResult);
+}
+
 NS_IMETHODIMP
 nsNullPrincipal::CheckMayLoad(nsIURI* aURI, bool aReport, bool aAllowIfInheritsPrincipal)
  {
diff --git a/caps/src/nsPrincipal.cpp b/caps/src/nsPrincipal.cpp
index 52a298f2eba9..ccd5b550a6a8 100644
--- a/caps/src/nsPrincipal.cpp
+++ b/caps/src/nsPrincipal.cpp
@@ -285,6 +285,12 @@ nsPrincipal::EqualsIgnoringDomain(nsIPrincipal *aOther, bool *aResult)
   return NS_OK;
 }
 
+NS_IMETHODIMP
+nsPrincipal::EqualsConsideringDomain(nsIPrincipal *aOther, bool *aResult)
+{
+  return Equals(aOther, aResult);
+}
+
 NS_IMETHODIMP
 nsPrincipal::Subsumes(nsIPrincipal *aOther, bool *aResult)
 {
@@ -297,6 +303,12 @@ nsPrincipal::SubsumesIgnoringDomain(nsIPrincipal *aOther, bool *aResult)
   return EqualsIgnoringDomain(aOther, aResult);
 }
 
+NS_IMETHODIMP
+nsPrincipal::SubsumesConsideringDomain(nsIPrincipal *aOther, bool *aResult)
+{
+  return Subsumes(aOther, aResult);
+}
+
 NS_IMETHODIMP
 nsPrincipal::GetURI(nsIURI** aURI)
 {
@@ -674,6 +686,12 @@ nsExpandedPrincipal::EqualsIgnoringDomain(nsIPrincipal* aOther, bool* aResult)
   return ::Equals(this, &nsIPrincipal::SubsumesIgnoringDomain, aOther, aResult);
 }
 
+NS_IMETHODIMP
+nsExpandedPrincipal::EqualsConsideringDomain(nsIPrincipal* aOther, bool* aResult)
+{
+  return ::Equals(this, &nsIPrincipal::SubsumesConsideringDomain, aOther, aResult);
+}
+
 // nsExpandedPrincipal::Subsumes and nsExpandedPrincipal::SubsumesIgnoringDomain
 // shares the same logic. The difference only that Subsumes calls are replaced
 //with SubsumesIgnoringDomain calls in the second case.
@@ -726,6 +744,12 @@ nsExpandedPrincipal::SubsumesIgnoringDomain(nsIPrincipal* aOther, bool* aResult)
   return ::Subsumes(this, &nsIPrincipal::SubsumesIgnoringDomain, aOther, aResult);
 }
 
+NS_IMETHODIMP
+nsExpandedPrincipal::SubsumesConsideringDomain(nsIPrincipal* aOther, bool* aResult)
+{
+  return ::Subsumes(this, &nsIPrincipal::SubsumesConsideringDomain, aOther, aResult);
+}
+
 NS_IMETHODIMP
 nsExpandedPrincipal::CheckMayLoad(nsIURI* uri, bool aReport, bool aAllowIfInheritsPrincipal)
 {
diff --git a/caps/src/nsSystemPrincipal.cpp b/caps/src/nsSystemPrincipal.cpp
index b5ae0421cb00..9fc9872b8114 100644
--- a/caps/src/nsSystemPrincipal.cpp
+++ b/caps/src/nsSystemPrincipal.cpp
@@ -84,6 +84,12 @@ nsSystemPrincipal::EqualsIgnoringDomain(nsIPrincipal *other, bool *result)
     return Equals(other, result);
 }
 
+NS_IMETHODIMP
+nsSystemPrincipal::EqualsConsideringDomain(nsIPrincipal *other, bool *result)
+{
+    return Equals(other, result);
+}
+
 NS_IMETHODIMP
 nsSystemPrincipal::Subsumes(nsIPrincipal *other, bool *result)
 {
@@ -98,6 +104,13 @@ nsSystemPrincipal::SubsumesIgnoringDomain(nsIPrincipal *other, bool *result)
     return NS_OK;
 }
 
+NS_IMETHODIMP
+nsSystemPrincipal::SubsumesConsideringDomain(nsIPrincipal *other, bool *result)
+{
+    *result = true;
+    return NS_OK;
+}
+
 NS_IMETHODIMP
 nsSystemPrincipal::CheckMayLoad(nsIURI* uri, bool aReport, bool aAllowIfInheritsPrincipal)
 {