--- a/xpcom/ds/nsISupportsArray.idl
+++ b/xpcom/ds/nsISupportsArray.idl
@@ -45,20 +45,18 @@ interface nsISupportsArray : nsICollecti
   long GetLastIndexOf(in nsISupports aPossibleElement);  
   
   [notxpcom] boolean InsertElementAt(in nsISupports aElement,
                                      in unsigned long aIndex);
   [notxpcom] boolean ReplaceElementAt(in nsISupports aElement,
                                       in unsigned long aIndex);
 
   [notxpcom] boolean RemoveElementAt(in unsigned long aIndex);
-  [notxpcom] boolean RemoveLastElement([const] in nsISupports aElement);
   
   // xpcom-compatible versions
-  void DeleteLastElement(in nsISupports aElement);
   void DeleteElementAt(in unsigned long aIndex);
   
   void Compact();
   
 
   nsISupportsArray clone();
 
   [notxpcom] boolean RemoveElementsAt(in unsigned long aIndex,

--- a/xpcom/ds/nsSupportsArray.cpp
+++ b/xpcom/ds/nsSupportsArray.cpp
@@ -315,28 +315,16 @@ nsSupportsArray::RemoveElement(nsISuppor
   int32_t theIndex = IndexOfStartingAt(aElement, 0);
   if (theIndex >= 0) {
     return RemoveElementAt(theIndex) ? NS_OK : NS_ERROR_FAILURE;
   }
 
   return NS_ERROR_FAILURE;
 }
 
-NS_IMETHODIMP_(bool)
-nsSupportsArray::RemoveLastElement(const nsISupports* aElement)
-{
-  int32_t theIndex = LastIndexOf(aElement);
-  if (theIndex >= 0) {
-    return RemoveElementAt(theIndex);
-  }
-
-  return false;
-}
-
-
 NS_IMETHODIMP
 nsSupportsArray::Clear(void)
 {
   if (0 < mCount) {
     do {
       --mCount;
       NS_IF_RELEASE(mArray[mCount]);
     } while (0 != mCount);

--- a/xpcom/ds/nsSupportsArray.h
+++ b/xpcom/ds/nsSupportsArray.h
@@ -90,23 +90,16 @@ public:
   MOZ_MUST_USE NS_IMETHOD_(bool)
   ReplaceElementAt(nsISupports* aElement, uint32_t aIndex) override;
 
   MOZ_MUST_USE NS_IMETHOD_(bool)
   RemoveElementAt(uint32_t aIndex) override
   {
     return RemoveElementsAt(aIndex, 1);
   }
-  MOZ_MUST_USE NS_IMETHOD_(bool)
-  RemoveLastElement(const nsISupports* aElement) override;
-
-  MOZ_MUST_USE NS_IMETHOD DeleteLastElement(nsISupports* aElement) override
-  {
-    return (RemoveLastElement(aElement) ? NS_OK : NS_ERROR_FAILURE);
-  }
 
   MOZ_MUST_USE NS_IMETHOD DeleteElementAt(uint32_t aIndex) override
   {
     return (RemoveElementAt(aIndex) ? NS_OK : NS_ERROR_FAILURE);
   }
 
   NS_IMETHOD Compact(void) override;
 

--- a/xpcom/glue/tests/gtest/TestArray.cpp
+++ b/xpcom/glue/tests/gtest/TestArray.cpp
@@ -133,29 +133,26 @@ TEST(Array, main)
     count--;
     EXPECT_EQ(index, expectedIndex[count]);
 
     // test ReplaceElementAt
     array->ReplaceElementAt(foo, 8);
     int32_t   replaceResult[13] = {3, 0, 1, 2, 3, 4, 3, 5, 3, 7, 8, 9, 3};
     CheckArray(array, 13, replaceResult, 9);
 
-    // test RemoveElementAt, RemoveElement RemoveLastElement
+    // test RemoveElementAt, RemoveElement
     array->RemoveElementAt(0);
     int32_t   removeResult[12] = {0, 1, 2, 3, 4, 3, 5, 3, 7, 8, 9, 3};
     CheckArray(array, 12, removeResult, 9);
     array->RemoveElementAt(7);
     int32_t   removeResult2[11] = {0, 1, 2, 3, 4, 3, 5, 7, 8, 9, 3};
     CheckArray(array, 11, removeResult2, 9);
     array->RemoveElement(foo);
     int32_t   removeResult3[10] = {0, 1, 2, 4, 3, 5, 7, 8, 9, 3};
     CheckArray(array, 10, removeResult3, 9);
-    array->RemoveLastElement(foo);
-    int32_t   removeResult4[9] = {0, 1, 2, 4, 3, 5, 7, 8, 9};
-    CheckArray(array, 9, removeResult4, 9);
 
     foo = nullptr;
 
     // test clear
     array->Clear();
     FillArray(array, 4);
     CheckArray(array, 4, fillResult, 4);