diff --git a/dom/html/nsHTMLDocument.cpp b/dom/html/nsHTMLDocument.cpp
index e01ebe76e4b1..7cb4482ac23b 100644
--- a/dom/html/nsHTMLDocument.cpp
+++ b/dom/html/nsHTMLDocument.cpp
@@ -4037,84 +4037,32 @@ return
 NS_OK
 ;
 }
-NS_IMETHODIMP
-nsHTMLDocument
-:
-:
-SetDomain
-(
-const
-nsAString
-&
-aDomain
-)
-{
-ErrorResult
-rv
-;
-SetDomain
-(
-aDomain
-rv
-)
-;
-return
-rv
-.
-StealNSResult
-(
-)
-;
-}
-void
+already_AddRefed
+<
+nsIURI
+>
 nsHTMLDocument
 :
 :
-SetDomain
+CreateInheritingURIForHost
 (
 const
-nsAString
-&
-aDomain
-ErrorResult
-&
-rv
-)
-{
-if
-(
-mSandboxFlags
+nsACString
 &
-SANDBOXED_DOMAIN
+aHostString
 )
 {
-rv
-.
-Throw
-(
-NS_ERROR_DOM_SECURITY_ERR
-)
-;
-return
-;
-}
 if
 (
-aDomain
+aHostString
 .
 IsEmpty
 (
 )
 )
 {
-rv
-.
-Throw
-(
-NS_ERROR_DOM_BAD_DOCUMENT_DOMAIN
-)
-;
 return
+nullptr
 ;
 }
 nsCOMPtr
@@ -4133,14 +4081,8 @@ if
 uri
 )
 {
-rv
-.
-Throw
-(
-NS_ERROR_FAILURE
-)
-;
 return
+nullptr
 ;
 }
 nsCOMPtr
@@ -4150,7 +4092,7 @@ nsIURI
 newURI
 ;
 nsresult
-rv2
+rv
 =
 uri
 -
@@ -4167,21 +4109,15 @@ if
 (
 NS_FAILED
 (
-rv2
+rv
 )
 )
 {
-rv
-.
-Throw
-(
-rv2
-)
-;
 return
+nullptr
 ;
 }
-rv2
+rv
 =
 newURI
 -
@@ -4197,93 +4133,94 @@ if
 (
 NS_FAILED
 (
-rv2
+rv
 )
 )
 {
-rv
-.
-Throw
-(
-rv2
-)
-;
 return
+nullptr
 ;
 }
-rv2
+rv
 =
 newURI
 -
 >
 SetHostAndPort
 (
-NS_ConvertUTF16toUTF8
-(
-aDomain
-)
+aHostString
 )
 ;
 if
 (
 NS_FAILED
 (
-rv2
+rv
 )
 )
 {
-rv
+return
+nullptr
+;
+}
+return
+newURI
 .
-Throw
+forget
 (
-rv2
 )
 ;
-return
-;
 }
-nsAutoCString
-current
-domain
-;
-if
-(
-NS_FAILED
-(
-uri
--
+already_AddRefed
+<
+nsIURI
 >
-GetAsciiHost
+nsHTMLDocument
+:
+:
+RegistrableDomainSuffixOfInternal
 (
-current
-)
-)
+const
+nsAString
+&
+aNewDomain
+nsIURI
+*
+aOrigHost
 )
-current
-.
-Truncate
+{
+nsAutoCString
+domain
+=
+NS_ConvertUTF16toUTF8
 (
+aNewDomain
 )
 ;
+nsAutoCString
+current
+;
 if
 (
 NS_FAILED
 (
-newURI
+aOrigHost
 -
 >
 GetAsciiHost
 (
-domain
+current
 )
 )
 )
-domain
+{
+current
 .
 Truncate
 (
 )
 ;
+}
 bool
 ok
 =
@@ -4358,14 +4295,8 @@ if
 tldService
 )
 {
-rv
-.
-Throw
-(
-NS_ERROR_NOT_AVAILABLE
-)
-;
 return
+nullptr
 ;
 }
 nsAutoCString
@@ -4380,7 +4311,7 @@ tldService
 >
 GetBaseDomain
 (
-uri
+aOrigHost
 0
 currentBaseDomain
 )
@@ -4450,6 +4381,217 @@ if
 ok
 )
 {
+return
+nullptr
+;
+}
+return
+CreateInheritingURIForHost
+(
+domain
+)
+;
+}
+bool
+nsHTMLDocument
+:
+:
+IsRegistrableDomainSuffixOfOrEqualTo
+(
+const
+nsAString
+&
+aHostSuffixString
+const
+nsACString
+&
+aOrigHost
+)
+{
+if
+(
+aHostSuffixString
+.
+IsEmpty
+(
+)
+)
+{
+return
+false
+;
+}
+nsCOMPtr
+<
+nsIURI
+>
+origURI
+=
+CreateInheritingURIForHost
+(
+aOrigHost
+)
+;
+if
+(
+!
+origURI
+)
+{
+return
+false
+;
+}
+nsCOMPtr
+<
+nsIURI
+>
+newURI
+=
+RegistrableDomainSuffixOfInternal
+(
+aHostSuffixString
+origURI
+)
+;
+if
+(
+!
+newURI
+)
+{
+return
+false
+;
+}
+return
+true
+;
+}
+NS_IMETHODIMP
+nsHTMLDocument
+:
+:
+SetDomain
+(
+const
+nsAString
+&
+aDomain
+)
+{
+ErrorResult
+rv
+;
+SetDomain
+(
+aDomain
+rv
+)
+;
+return
+rv
+.
+StealNSResult
+(
+)
+;
+}
+void
+nsHTMLDocument
+:
+:
+SetDomain
+(
+const
+nsAString
+&
+aDomain
+ErrorResult
+&
+rv
+)
+{
+if
+(
+mSandboxFlags
+&
+SANDBOXED_DOMAIN
+)
+{
+rv
+.
+Throw
+(
+NS_ERROR_DOM_SECURITY_ERR
+)
+;
+return
+;
+}
+if
+(
+aDomain
+.
+IsEmpty
+(
+)
+)
+{
+rv
+.
+Throw
+(
+NS_ERROR_DOM_BAD_DOCUMENT_DOMAIN
+)
+;
+return
+;
+}
+nsCOMPtr
+<
+nsIURI
+>
+uri
+=
+GetDomainURI
+(
+)
+;
+if
+(
+!
+uri
+)
+{
+rv
+.
+Throw
+(
+NS_ERROR_FAILURE
+)
+;
+return
+;
+}
+nsCOMPtr
+<
+nsIURI
+>
+newURI
+=
+RegistrableDomainSuffixOfInternal
+(
+aDomain
+uri
+)
+;
+if
+(
+!
+newURI
+)
+{
 rv
 .
 Throw
diff --git a/dom/html/nsHTMLDocument.h b/dom/html/nsHTMLDocument.h
index 3c6db7a1393f..fec0fa74295e 100644
--- a/dom/html/nsHTMLDocument.h
+++ b/dom/html/nsHTMLDocument.h
@@ -680,6 +680,19 @@ ErrorResult
 rv
 )
 ;
+bool
+IsRegistrableDomainSuffixOfOrEqualTo
+(
+const
+nsAString
+&
+aHostSuffixString
+const
+nsACString
+&
+aOrigHost
+)
+;
 void
 GetCookie
 (
@@ -1362,6 +1375,33 @@ GetDomainURI
 (
 )
 ;
+already_AddRefed
+<
+nsIURI
+>
+CreateInheritingURIForHost
+(
+const
+nsACString
+&
+aHostString
+)
+;
+already_AddRefed
+<
+nsIURI
+>
+RegistrableDomainSuffixOfInternal
+(
+const
+nsAString
+&
+aHostSuffixString
+nsIURI
+*
+aOrigHost
+)
+;
 nsresult
 WriteCommon
 (