diff --git a/dom/base/nsDOMClassInfo.cpp b/dom/base/nsDOMClassInfo.cpp
index 5d2956c6b6c..54ae26c9123 100644
--- a/dom/base/nsDOMClassInfo.cpp
+++ b/dom/base/nsDOMClassInfo.cpp
@@ -43,7 +43,6 @@
 #include "nsIDOMDocument.h"
 #include "nsIDOMEvent.h"
 #include "nsIDOMEventListener.h"
-#include "nsIProgrammingLanguage.h"
 #include "nsContentUtils.h"
 #include "nsIDOMGlobalPropertyInitializer.h"
 #include "mozilla/Attributes.h"
@@ -864,14 +863,6 @@ nsDOMClassInfo::GetClassIDNoAlloc(nsCID *aClassID)
   return NS_ERROR_NOT_AVAILABLE;
 }
 
-NS_IMETHODIMP
-nsDOMClassInfo::GetImplementationLanguage(uint32_t *aImplLanguage)
-{
-  *aImplLanguage = nsIProgrammingLanguage::CPLUSPLUS;
-
-  return NS_OK;
-}
-
 NS_IMETHODIMP
 nsDOMClassInfo::GetFlags(uint32_t *aFlags)
 {
diff --git a/dom/base/nsHostObjectURI.cpp b/dom/base/nsHostObjectURI.cpp
index 1d48685c744..64de0c6f025 100644
--- a/dom/base/nsHostObjectURI.cpp
+++ b/dom/base/nsHostObjectURI.cpp
@@ -8,7 +8,6 @@
 #include "nsAutoPtr.h"
 #include "nsIObjectInputStream.h"
 #include "nsIObjectOutputStream.h"
-#include "nsIProgrammingLanguage.h"
 
 #include "mozilla/ipc/BackgroundUtils.h"
 #include "mozilla/ipc/URIUtils.h"
@@ -235,13 +234,6 @@ nsHostObjectURI::GetClassID(nsCID * *aClassID)
   return GetClassIDNoAlloc(*aClassID);
 }
 
-NS_IMETHODIMP 
-nsHostObjectURI::GetImplementationLanguage(uint32_t *aImplementationLanguage)
-{
-  *aImplementationLanguage = nsIProgrammingLanguage::CPLUSPLUS;
-  return NS_OK;
-}
-
 NS_IMETHODIMP 
 nsHostObjectURI::GetFlags(uint32_t *aFlags)
 {
diff --git a/js/xpconnect/loader/XPCOMUtils.jsm b/js/xpconnect/loader/XPCOMUtils.jsm
index 184069754bb..a3287ab408f 100644
--- a/js/xpconnect/loader/XPCOMUtils.jsm
+++ b/js/xpconnect/loader/XPCOMUtils.jsm
@@ -148,7 +148,6 @@ this.XPCOMUtils = {
       contractID: classInfo.contractID,
       classDescription: classInfo.classDescription,
       classID: classInfo.classID,
-      implementationLanguage: Ci.nsIProgrammingLanguage.JAVASCRIPT,
       flags: classInfo.flags,
       QueryInterface: this.generateQI([Ci.nsIClassInfo])
     };
diff --git a/js/xpconnect/src/XPCComponents.cpp b/js/xpconnect/src/XPCComponents.cpp
index 7689787a205..564e24607eb 100644
--- a/js/xpconnect/src/XPCComponents.cpp
+++ b/js/xpconnect/src/XPCComponents.cpp
@@ -30,7 +30,6 @@
 #include "nsZipArchive.h"
 #include "nsIDOMFile.h"
 #include "nsIDOMFileList.h"
-#include "nsIProgrammingLanguage.h"
 #include "nsWindowMemoryReporter.h"
 #include "nsDOMClassInfo.h"
 #include "ShimInterfaceInfo.h"
@@ -187,14 +186,6 @@ nsXPCComponents_Interfaces::GetClassID(nsCID * *aClassID)
     return NS_OK;
 }
 
-/* readonly attribute uint32_t implementationLanguage; */
-NS_IMETHODIMP
-nsXPCComponents_Interfaces::GetImplementationLanguage(uint32_t* aImplementationLanguage)
-{
-    *aImplementationLanguage = nsIProgrammingLanguage::CPLUSPLUS;
-    return NS_OK;
-}
-
 /* readonly attribute uint32_t flags; */
 NS_IMETHODIMP
 nsXPCComponents_Interfaces::GetFlags(uint32_t* aFlags)
@@ -430,14 +421,6 @@ nsXPCComponents_InterfacesByID::GetClassID(nsCID * *aClassID)
     return NS_OK;
 }
 
-/* readonly attribute uint32_t implementationLanguage; */
-NS_IMETHODIMP
-nsXPCComponents_InterfacesByID::GetImplementationLanguage(uint32_t* aImplementationLanguage)
-{
-    *aImplementationLanguage = nsIProgrammingLanguage::CPLUSPLUS;
-    return NS_OK;
-}
-
 /* readonly attribute uint32_t flags; */
 NS_IMETHODIMP
 nsXPCComponents_InterfacesByID::GetFlags(uint32_t* aFlags)
@@ -675,14 +658,6 @@ nsXPCComponents_Classes::GetClassID(nsCID * *aClassID)
     return NS_OK;
 }
 
-/* readonly attribute uint32_t implementationLanguage; */
-NS_IMETHODIMP
-nsXPCComponents_Classes::GetImplementationLanguage(uint32_t* aImplementationLanguage)
-{
-    *aImplementationLanguage = nsIProgrammingLanguage::CPLUSPLUS;
-    return NS_OK;
-}
-
 /* readonly attribute uint32_t flags; */
 NS_IMETHODIMP
 nsXPCComponents_Classes::GetFlags(uint32_t* aFlags)
@@ -900,14 +875,6 @@ nsXPCComponents_ClassesByID::GetClassID(nsCID * *aClassID)
     return NS_OK;
 }
 
-/* readonly attribute uint32_t implementationLanguage; */
-NS_IMETHODIMP
-nsXPCComponents_ClassesByID::GetImplementationLanguage(uint32_t* aImplementationLanguage)
-{
-    *aImplementationLanguage = nsIProgrammingLanguage::CPLUSPLUS;
-    return NS_OK;
-}
-
 /* readonly attribute uint32_t flags; */
 NS_IMETHODIMP
 nsXPCComponents_ClassesByID::GetFlags(uint32_t* aFlags)
@@ -1148,14 +1115,6 @@ nsXPCComponents_Results::GetClassID(nsCID * *aClassID)
     return NS_OK;
 }
 
-/* readonly attribute uint32_t implementationLanguage; */
-NS_IMETHODIMP
-nsXPCComponents_Results::GetImplementationLanguage(uint32_t* aImplementationLanguage)
-{
-    *aImplementationLanguage = nsIProgrammingLanguage::CPLUSPLUS;
-    return NS_OK;
-}
-
 /* readonly attribute uint32_t flags; */
 NS_IMETHODIMP
 nsXPCComponents_Results::GetFlags(uint32_t* aFlags)
@@ -1353,14 +1312,6 @@ nsXPCComponents_ID::GetClassID(nsCID * *aClassID)
     return NS_OK;
 }
 
-/* readonly attribute uint32_t implementationLanguage; */
-NS_IMETHODIMP
-nsXPCComponents_ID::GetImplementationLanguage(uint32_t* aImplementationLanguage)
-{
-    *aImplementationLanguage = nsIProgrammingLanguage::CPLUSPLUS;
-    return NS_OK;
-}
-
 /* readonly attribute uint32_t flags; */
 NS_IMETHODIMP
 nsXPCComponents_ID::GetFlags(uint32_t* aFlags)
@@ -1569,14 +1520,6 @@ nsXPCComponents_Exception::GetClassID(nsCID * *aClassID)
     return NS_OK;
 }
 
-/* readonly attribute uint32_t implementationLanguage; */
-NS_IMETHODIMP
-nsXPCComponents_Exception::GetImplementationLanguage(uint32_t* aImplementationLanguage)
-{
-    *aImplementationLanguage = nsIProgrammingLanguage::CPLUSPLUS;
-    return NS_OK;
-}
-
 /* readonly attribute uint32_t flags; */
 NS_IMETHODIMP
 nsXPCComponents_Exception::GetFlags(uint32_t* aFlags)
@@ -1958,14 +1901,6 @@ nsXPCConstructor::GetClassID(nsCID * *aClassID)
     return NS_OK;
 }
 
-/* readonly attribute uint32_t implementationLanguage; */
-NS_IMETHODIMP
-nsXPCConstructor::GetImplementationLanguage(uint32_t* aImplementationLanguage)
-{
-    *aImplementationLanguage = nsIProgrammingLanguage::CPLUSPLUS;
-    return NS_OK;
-}
-
 /* readonly attribute uint32_t flags; */
 NS_IMETHODIMP
 nsXPCConstructor::GetFlags(uint32_t* aFlags)
@@ -2212,14 +2147,6 @@ nsXPCComponents_Constructor::GetClassID(nsCID * *aClassID)
     return NS_OK;
 }
 
-/* readonly attribute uint32_t implementationLanguage; */
-NS_IMETHODIMP
-nsXPCComponents_Constructor::GetImplementationLanguage(uint32_t* aImplementationLanguage)
-{
-    *aImplementationLanguage = nsIProgrammingLanguage::CPLUSPLUS;
-    return NS_OK;
-}
-
 /* readonly attribute uint32_t flags; */
 NS_IMETHODIMP
 nsXPCComponents_Constructor::GetFlags(uint32_t* aFlags)
diff --git a/js/xpconnect/src/XPCRuntimeService.cpp b/js/xpconnect/src/XPCRuntimeService.cpp
index 7797f483fe0..239851fa972 100644
--- a/js/xpconnect/src/XPCRuntimeService.cpp
+++ b/js/xpconnect/src/XPCRuntimeService.cpp
@@ -8,7 +8,6 @@
 
 #include "nsContentUtils.h"
 #include "BackstagePass.h"
-#include "nsIProgrammingLanguage.h"
 #include "nsDOMClassInfo.h"
 #include "nsIPrincipal.h"
 #include "mozilla/dom/BindingUtils.h"
@@ -148,14 +147,6 @@ BackstagePass::GetClassID(nsCID * *aClassID)
     return NS_OK;
 }
 
-/* readonly attribute uint32_t implementationLanguage; */
-NS_IMETHODIMP
-BackstagePass::GetImplementationLanguage(uint32_t* aImplementationLanguage)
-{
-    *aImplementationLanguage = nsIProgrammingLanguage::CPLUSPLUS;
-    return NS_OK;
-}
-
 /* readonly attribute uint32_t flags; */
 NS_IMETHODIMP
 BackstagePass::GetFlags(uint32_t* aFlags)
diff --git a/js/xpconnect/tests/unit/component-blob.js b/js/xpconnect/tests/unit/component-blob.js
index 3771a736688..fd528c86be7 100644
--- a/js/xpconnect/tests/unit/component-blob.js
+++ b/js/xpconnect/tests/unit/component-blob.js
@@ -59,7 +59,6 @@ BlobComponent.prototype =
   contractID: "@mozilla.org/tests/component-blob;1",
 
   // nsIClassInfo
-  implementationLanguage: Components.interfaces.nsIProgrammingLanguage.JAVASCRIPT,
   flags: 0,
 
   getInterfaces: function getInterfaces(aCount) {
diff --git a/js/xpconnect/tests/unit/component-file.js b/js/xpconnect/tests/unit/component-file.js
index 21496368a74..6a1b6ac8d77 100644
--- a/js/xpconnect/tests/unit/component-file.js
+++ b/js/xpconnect/tests/unit/component-file.js
@@ -84,7 +84,6 @@ FileComponent.prototype =
   contractID: "@mozilla.org/tests/component-file;1",
 
   // nsIClassInfo
-  implementationLanguage: Components.interfaces.nsIProgrammingLanguage.JAVASCRIPT,
   flags: 0,
 
   getInterfaces: function getInterfaces(aCount) {
diff --git a/js/xpconnect/tests/unit/component_import.js b/js/xpconnect/tests/unit/component_import.js
index 7b9ad935fcf..8d7e3d0cf6c 100644
--- a/js/xpconnect/tests/unit/component_import.js
+++ b/js/xpconnect/tests/unit/component_import.js
@@ -15,7 +15,6 @@ FooComponent.prototype =
   contractID:       "@mozilla.org/tests/module-importer;1",
 
   // nsIClassInfo
-  implementationLanguage: Components.interfaces.nsIProgrammingLanguage.JAVASCRIPT,
   flags: 0,
 
   getInterfaces: function getInterfaces(aCount) {
@@ -28,10 +27,10 @@ FooComponent.prototype =
       thereIsNoSuchIdentifier;
       threw = false;
     } catch (ex) {
-      do_check_true(ex.lineNumber == 28);
+      do_check_true(ex.lineNumber == 27);
     }
     do_check_true(threw);
-    
+
     return interfaces;
   },
 
@@ -59,7 +58,6 @@ BarComponent.prototype =
   contractID: "@mozilla.org/tests/module-importer;2",
 
   // nsIClassInfo
-  implementationLanguage: Components.interfaces.nsIProgrammingLanguage.JAVASCRIPT,
   flags: 0,
 
   getInterfaces: function getInterfaces(aCount) {
diff --git a/modules/libjar/nsJARURI.cpp b/modules/libjar/nsJARURI.cpp
index bad046024e3..ecf987d9883 100644
--- a/modules/libjar/nsJARURI.cpp
+++ b/modules/libjar/nsJARURI.cpp
@@ -19,7 +19,6 @@
 #include "nsNetCID.h"
 #include "nsIObjectInputStream.h"
 #include "nsIObjectOutputStream.h"
-#include "nsIProgrammingLanguage.h"
 #include "mozilla/ipc/URIUtils.h"
 
 using namespace mozilla::ipc;
@@ -195,13 +194,6 @@ nsJARURI::GetClassID(nsCID * *aClassID)
     return GetClassIDNoAlloc(*aClassID);
 }
 
-NS_IMETHODIMP 
-nsJARURI::GetImplementationLanguage(uint32_t *aImplementationLanguage)
-{
-    *aImplementationLanguage = nsIProgrammingLanguage::CPLUSPLUS;
-    return NS_OK;
-}
-
 NS_IMETHODIMP 
 nsJARURI::GetFlags(uint32_t *aFlags)
 {
diff --git a/netwerk/base/nsSimpleURI.cpp b/netwerk/base/nsSimpleURI.cpp
index e0054557c3d..bd7e4134696 100644
--- a/netwerk/base/nsSimpleURI.cpp
+++ b/netwerk/base/nsSimpleURI.cpp
@@ -18,7 +18,6 @@
 #include "nsIObjectOutputStream.h"
 #include "nsEscape.h"
 #include "nsError.h"
-#include "nsIProgrammingLanguage.h"
 #include "nsIIPCSerializableURI.h"
 #include "mozilla/MemoryReporting.h"
 #include "mozilla/ipc/URIUtils.h"
@@ -590,13 +589,6 @@ nsSimpleURI::GetClassID(nsCID * *aClassID)
     return GetClassIDNoAlloc(*aClassID);
 }
 
-NS_IMETHODIMP 
-nsSimpleURI::GetImplementationLanguage(uint32_t *aImplementationLanguage)
-{
-    *aImplementationLanguage = nsIProgrammingLanguage::CPLUSPLUS;
-    return NS_OK;
-}
-
 NS_IMETHODIMP 
 nsSimpleURI::GetFlags(uint32_t *aFlags)
 {
diff --git a/netwerk/base/nsSocketTransport2.cpp b/netwerk/base/nsSocketTransport2.cpp
index f83f9764b31..a05960f3330 100644
--- a/netwerk/base/nsSocketTransport2.cpp
+++ b/netwerk/base/nsSocketTransport2.cpp
@@ -28,7 +28,6 @@
 #include "nsISocketProvider.h"
 #include "nsISSLSocketControl.h"
 #include "nsIPipe.h"
-#include "nsIProgrammingLanguage.h"
 #include "nsIClassInfoImpl.h"
 #include "nsURLHelper.h"
 #include "nsIDNSService.h"
@@ -2466,13 +2465,6 @@ nsSocketTransport::GetClassID(nsCID * *aClassID)
     return NS_OK;
 }
 
-NS_IMETHODIMP
-nsSocketTransport::GetImplementationLanguage(uint32_t *aImplementationLanguage)
-{
-    *aImplementationLanguage = nsIProgrammingLanguage::CPLUSPLUS;
-    return NS_OK;
-}
-
 NS_IMETHODIMP
 nsSocketTransport::GetFlags(uint32_t *aFlags)
 {
diff --git a/netwerk/base/nsStandardURL.cpp b/netwerk/base/nsStandardURL.cpp
index 371415633db..06291e118c5 100644
--- a/netwerk/base/nsStandardURL.cpp
+++ b/netwerk/base/nsStandardURL.cpp
@@ -17,7 +17,6 @@
 #include "nsIIDNService.h"
 #include "prlog.h"
 #include "nsAutoPtr.h"
-#include "nsIProgrammingLanguage.h"
 #include "nsIURLParser.h"
 #include "nsNetCID.h"
 #include "mozilla/MemoryReporting.h"
@@ -3208,13 +3207,6 @@ nsStandardURL::GetClassID(nsCID * *aClassID)
     return GetClassIDNoAlloc(*aClassID);
 }
 
-NS_IMETHODIMP 
-nsStandardURL::GetImplementationLanguage(uint32_t *aImplementationLanguage)
-{
-    *aImplementationLanguage = nsIProgrammingLanguage::CPLUSPLUS;
-    return NS_OK;
-}
-
 NS_IMETHODIMP 
 nsStandardURL::GetFlags(uint32_t *aFlags)
 {
diff --git a/security/manager/ssl/src/TransportSecurityInfo.cpp b/security/manager/ssl/src/TransportSecurityInfo.cpp
index 568ce5415ee..d3d8e11dac9 100644
--- a/security/manager/ssl/src/TransportSecurityInfo.cpp
+++ b/security/manager/ssl/src/TransportSecurityInfo.cpp
@@ -17,7 +17,6 @@
 #include "nsIObjectInputStream.h"
 #include "nsIObjectOutputStream.h"
 #include "nsNSSCertHelper.h"
-#include "nsIProgrammingLanguage.h"
 #include "nsIArray.h"
 #include "nsComponentManagerUtils.h"
 #include "nsReadableUtils.h"
@@ -476,14 +475,6 @@ TransportSecurityInfo::GetClassID(nsCID * *aClassID)
   return GetClassIDNoAlloc(*aClassID);
 }
 
-NS_IMETHODIMP
-TransportSecurityInfo::GetImplementationLanguage(
-  uint32_t *aImplementationLanguage)
-{
-  *aImplementationLanguage = nsIProgrammingLanguage::CPLUSPLUS;
-  return NS_OK;
-}
-
 NS_IMETHODIMP
 TransportSecurityInfo::GetFlags(uint32_t *aFlags)
 {
diff --git a/security/manager/ssl/src/nsNSSCertificate.cpp b/security/manager/ssl/src/nsNSSCertificate.cpp
index bb3c8983b74..1fc86818dad 100644
--- a/security/manager/ssl/src/nsNSSCertificate.cpp
+++ b/security/manager/ssl/src/nsNSSCertificate.cpp
@@ -36,7 +36,6 @@
 #include "nsCertVerificationThread.h"
 #include "nsIObjectOutputStream.h"
 #include "nsIObjectInputStream.h"
-#include "nsIProgrammingLanguage.h"
 #include "nsXULAppAPI.h"
 #include "nsProxyRelease.h"
 #include "mozilla/Base64.h"
@@ -1950,13 +1949,6 @@ nsNSSCertificate::GetClassID(nsCID** aClassID)
   return GetClassIDNoAlloc(*aClassID);
 }
 
-NS_IMETHODIMP
-nsNSSCertificate::GetImplementationLanguage(uint32_t* aImplementationLanguage)
-{
-  *aImplementationLanguage = nsIProgrammingLanguage::CPLUSPLUS;
-  return NS_OK;
-}
-
 NS_IMETHODIMP
 nsNSSCertificate::GetFlags(uint32_t* aFlags)
 {
diff --git a/security/manager/ssl/src/nsNSSCertificateFakeTransport.cpp b/security/manager/ssl/src/nsNSSCertificateFakeTransport.cpp
index fd278c16951..15b24a766b5 100644
--- a/security/manager/ssl/src/nsNSSCertificateFakeTransport.cpp
+++ b/security/manager/ssl/src/nsNSSCertificateFakeTransport.cpp
@@ -8,7 +8,6 @@
 #include "nsIClassInfoImpl.h"
 #include "nsIObjectInputStream.h"
 #include "nsIObjectOutputStream.h"
-#include "nsIProgrammingLanguage.h"
 #include "nsISupportsPrimitives.h"
 #include "nsNSSCertificate.h"
 #include "nsString.h"
@@ -319,14 +318,6 @@ nsNSSCertificateFakeTransport::GetClassID(nsCID** aClassID)
   return GetClassIDNoAlloc(*aClassID);
 }
 
-NS_IMETHODIMP
-nsNSSCertificateFakeTransport::GetImplementationLanguage(
-  uint32_t* aImplementationLanguage)
-{
-  *aImplementationLanguage = nsIProgrammingLanguage::CPLUSPLUS;
-  return NS_OK;
-}
-
 NS_IMETHODIMP
 nsNSSCertificateFakeTransport::GetFlags(uint32_t* aFlags)
 {
diff --git a/security/manager/ssl/src/nsSSLStatus.cpp b/security/manager/ssl/src/nsSSLStatus.cpp
index adcfba18be7..369413385b2 100644
--- a/security/manager/ssl/src/nsSSLStatus.cpp
+++ b/security/manager/ssl/src/nsSSLStatus.cpp
@@ -7,7 +7,6 @@
 #include "nsSSLStatus.h"
 #include "plstr.h"
 #include "nsIClassInfoImpl.h"
-#include "nsIProgrammingLanguage.h"
 #include "nsIObjectOutputStream.h"
 #include "nsIObjectInputStream.h"
 #include "ssl.h"
@@ -244,13 +243,6 @@ nsSSLStatus::GetClassID(nsCID** aClassID)
   return GetClassIDNoAlloc(*aClassID);
 }
 
-NS_IMETHODIMP
-nsSSLStatus::GetImplementationLanguage(uint32_t* aImplementationLanguage)
-{
-  *aImplementationLanguage = nsIProgrammingLanguage::CPLUSPLUS;
-  return NS_OK;
-}
-
 NS_IMETHODIMP
 nsSSLStatus::GetFlags(uint32_t* aFlags)
 {
diff --git a/storage/src/mozStorageAsyncStatement.cpp b/storage/src/mozStorageAsyncStatement.cpp
index cc7671d17b5..de0f3198fa8 100644
--- a/storage/src/mozStorageAsyncStatement.cpp
+++ b/storage/src/mozStorageAsyncStatement.cpp
@@ -12,7 +12,6 @@
 #include "nsProxyRelease.h"
 #include "nsThreadUtils.h"
 #include "nsIClassInfoImpl.h"
-#include "nsIProgrammingLanguage.h"
 #include "Variant.h"
 
 #include "mozIStorageError.h"
@@ -86,13 +85,6 @@ public:
     return NS_OK;
   }
 
-  NS_IMETHODIMP
-  GetImplementationLanguage(uint32_t *_language) override
-  {
-    *_language = nsIProgrammingLanguage::CPLUSPLUS;
-    return NS_OK;
-  }
-
   NS_IMETHODIMP
   GetFlags(uint32_t *_flags) override
   {
diff --git a/storage/src/mozStorageStatement.cpp b/storage/src/mozStorageStatement.cpp
index 33efdf52bce..8155056d621 100644
--- a/storage/src/mozStorageStatement.cpp
+++ b/storage/src/mozStorageStatement.cpp
@@ -11,7 +11,6 @@
 #include "nsMemory.h"
 #include "nsThreadUtils.h"
 #include "nsIClassInfoImpl.h"
-#include "nsIProgrammingLanguage.h"
 #include "Variant.h"
 
 #include "mozIStorageError.h"
@@ -88,13 +87,6 @@ public:
     return NS_OK;
   }
 
-  NS_IMETHODIMP
-  GetImplementationLanguage(uint32_t *_language) override
-  {
-    *_language = nsIProgrammingLanguage::CPLUSPLUS;
-    return NS_OK;
-  }
-
   NS_IMETHODIMP
   GetFlags(uint32_t *_flags) override
   {
diff --git a/toolkit/modules/tests/xpcshell/test_GMPInstallManager.js b/toolkit/modules/tests/xpcshell/test_GMPInstallManager.js
index fa10edf6dd9..1c5a18493e1 100644
--- a/toolkit/modules/tests/xpcshell/test_GMPInstallManager.js
+++ b/toolkit/modules/tests/xpcshell/test_GMPInstallManager.js
@@ -753,7 +753,6 @@ xhr.prototype = {
     eval("this._on" + aEvent + " = aValue");
   },
   flags: Ci.nsIClassInfo.SINGLETON,
-  implementationLanguage: Ci.nsIProgrammingLanguage.JAVASCRIPT,
   getScriptableHelper: function() null,
   getInterfaces: function(aCount) {
     let interfaces = [Ci.nsISupports];
diff --git a/toolkit/mozapps/update/tests/data/xpcshellUtilsAUS.js b/toolkit/mozapps/update/tests/data/xpcshellUtilsAUS.js
index 1289f0e57f6..bc0709c9519 100644
--- a/toolkit/mozapps/update/tests/data/xpcshellUtilsAUS.js
+++ b/toolkit/mozapps/update/tests/data/xpcshellUtilsAUS.js
@@ -3028,7 +3028,6 @@ xhr.prototype = {
     eval("this._on" + aEvent + " = aValue");
   },
   flags: Ci.nsIClassInfo.SINGLETON,
-  implementationLanguage: Ci.nsIProgrammingLanguage.JAVASCRIPT,
   getScriptableHelper: function() null,
   getInterfaces: function(aCount) {
     let interfaces = [Ci.nsISupports];
@@ -3076,7 +3075,6 @@ function UpdatePrompt(aCallback) {
 
 UpdatePrompt.prototype = {
   flags: Ci.nsIClassInfo.SINGLETON,
-  implementationLanguage: Ci.nsIProgrammingLanguage.JAVASCRIPT,
   getScriptableHelper: function() null,
   getInterfaces: function(aCount) {
     let interfaces = [Ci.nsISupports, Ci.nsIUpdatePrompt];
diff --git a/xpcom/components/nsIClassInfo.idl b/xpcom/components/nsIClassInfo.idl
index 7afbd0d7d54..639d12aa874 100644
--- a/xpcom/components/nsIClassInfo.idl
+++ b/xpcom/components/nsIClassInfo.idl
@@ -14,7 +14,7 @@ interface nsIXPCScriptable;
  * instructions--you most likely do not want to inherit from nsIClassInfo.
  */
 
-[scriptable, uuid(7a633335-18cc-4794-9ddd-26ac7cab7be6)]
+[scriptable, uuid(a60569d7-d401-4677-ba63-2aa5971af25d)]
 interface nsIClassInfo : nsISupports
 {
     /**
@@ -51,12 +51,6 @@ interface nsIClassInfo : nsISupports
      */
     readonly attribute nsCIDPtr classID;
 
-    /**
-     * Return language type from list in nsIProgrammingLanguage
-     */
-
-    readonly attribute uint32_t implementationLanguage;
-
     /**
      * Bitflags for 'flags' attribute.
      */
@@ -72,7 +66,7 @@ interface nsIClassInfo : nsISupports
      * nsIContent.
      */
     const uint32_t CONTENT_NODE         = 1 << 6;
-    
+
     // The high order bit is RESERVED for consumers of these flags. 
     // No implementor of this interface should ever return flags 
     // with this bit set.
diff --git a/xpcom/glue/nsClassInfoImpl.cpp b/xpcom/glue/nsClassInfoImpl.cpp
index f0bda3400f2..6eb34f9f7c8 100644
--- a/xpcom/glue/nsClassInfoImpl.cpp
+++ b/xpcom/glue/nsClassInfoImpl.cpp
@@ -5,7 +5,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "nsIClassInfoImpl.h"
-#include "nsIProgrammingLanguage.h"
 
 NS_IMETHODIMP_(MozExternalRefCountType)
 GenericClassInfo::AddRef()
@@ -59,13 +58,6 @@ GenericClassInfo::GetClassID(nsCID** aClassID)
   return NS_ERROR_NOT_IMPLEMENTED;
 }
 
-NS_IMETHODIMP
-GenericClassInfo::GetImplementationLanguage(uint32_t* aLanguage)
-{
-  *aLanguage = nsIProgrammingLanguage::CPLUSPLUS;
-  return NS_OK;
-}
-
 NS_IMETHODIMP
 GenericClassInfo::GetFlags(uint32_t* aFlags)
 {
diff --git a/xpcom/glue/nsISupportsImpl.h b/xpcom/glue/nsISupportsImpl.h
index f886afb80ef..250a447cefb 100644
--- a/xpcom/glue/nsISupportsImpl.h
+++ b/xpcom/glue/nsISupportsImpl.h
@@ -1109,13 +1109,6 @@ _class::GetClassID(nsCID** _classID)                                          \
 }                                                                             \
                                                                               \
 NS_IMETHODIMP                                                                 \
-_class::GetImplementationLanguage(uint32_t* _language)                        \
-{                                                                             \
-  *_language = nsIProgrammingLanguage::CPLUSPLUS;                             \
-  return NS_OK;                                                               \
-}                                                                             \
-                                                                              \
-NS_IMETHODIMP                                                                 \
 _class::GetFlags(uint32_t* _flags)                                            \
 {                                                                             \
   *_flags = nsIClassInfo::THREADSAFE;                                         \
diff --git a/xpcom/io/nsPipe3.cpp b/xpcom/io/nsPipe3.cpp
index 9d88c383da6..9a96c286dca 100644
--- a/xpcom/io/nsPipe3.cpp
+++ b/xpcom/io/nsPipe3.cpp
@@ -11,7 +11,6 @@
 #include "nsIPipe.h"
 #include "nsIEventTarget.h"
 #include "nsISeekableStream.h"
-#include "nsIProgrammingLanguage.h"
 #include "nsRefPtr.h"
 #include "nsSegmentedBuffer.h"
 #include "nsStreamUtils.h"
diff --git a/xpcom/threads/nsThread.cpp b/xpcom/threads/nsThread.cpp
index 638b1a6e33a..6c2706bb4c0 100644
--- a/xpcom/threads/nsThread.cpp
+++ b/xpcom/threads/nsThread.cpp
@@ -153,13 +153,6 @@ nsThreadClassInfo::GetClassID(nsCID** aResult)
   return NS_OK;
 }
 
-NS_IMETHODIMP
-nsThreadClassInfo::GetImplementationLanguage(uint32_t* aResult)
-{
-  *aResult = nsIProgrammingLanguage::CPLUSPLUS;
-  return NS_OK;
-}
-
 NS_IMETHODIMP
 nsThreadClassInfo::GetFlags(uint32_t* aResult)
 {