--- a/memory/mozjemalloc/mozjemalloc.cpp
+++ b/memory/mozjemalloc/mozjemalloc.cpp
@@ -205,19 +205,16 @@ typedef long ssize_t;
 
 #define	MALLOC_DECOMMIT
 #endif
 
 #ifndef MOZ_MEMORY_WINDOWS
 #ifndef MOZ_MEMORY_SOLARIS
 #include <sys/cdefs.h>
 #endif
-#ifndef __DECONST
-#  define __DECONST(type, var)	((type)(uintptr_t)(const void *)(var))
-#endif
 #include <sys/mman.h>
 #ifndef MADV_FREE
 #  define MADV_FREE	MADV_DONTNEED
 #endif
 #ifndef MAP_NOSYNC
 #  define MAP_NOSYNC	0
 #endif
 #include <sys/param.h>
@@ -315,20 +312,16 @@ void *_mmap(void *addr, size_t length, i
 #ifdef MOZ_MEMORY_DARWIN
 static pthread_key_t tlsIndex;
 #endif
 
 #if defined(MOZ_MEMORY_SOLARIS) && defined(MAP_ALIGN) && !defined(JEMALLOC_NEVER_USES_MAP_ALIGN)
 #define JEMALLOC_USES_MAP_ALIGN	 /* Required on Solaris 10. Might improve performance elsewhere. */
 #endif
 
-#ifndef __DECONST
-#define __DECONST(type, var) ((type)(uintptr_t)(const void *)(var))
-#endif
-
 #ifdef MOZ_MEMORY_WINDOWS
    /* MSVC++ does not support C99 variable-length arrays. */
 #  define RB_NO_C99_VARARRAYS
 #endif
 #include "rb.h"
 
 #ifdef MOZ_DEBUG
    /* Disable inlining to make debugging easier. */
@@ -3816,17 +3809,17 @@ isalloc(const void *ptr)
 	} else {
 		extent_node_t *node, key;
 
 		/* Chunk (huge allocation). */
 
 		malloc_mutex_lock(&huge_mtx);
 
 		/* Extract from tree of huge allocations. */
-		key.addr = __DECONST(void *, ptr);
+		key.addr = const_cast<void*>(ptr);
 		node = extent_tree_ad_search(&huge, &key);
 		RELEASE_ASSERT(node != NULL);
 
 		ret = node->size;
 
 		malloc_mutex_unlock(&huge_mtx);
 	}
 
@@ -4398,17 +4391,17 @@ huge_ralloc(void *ptr, size_t size, size
 		if (psize < oldsize) {
 			extent_node_t *node, key;
 
 			pages_decommit((void *)((uintptr_t)ptr + psize),
 			    oldsize - psize);
 
 			/* Update recorded size. */
 			malloc_mutex_lock(&huge_mtx);
-			key.addr = __DECONST(void *, ptr);
+			key.addr = const_cast<void*>(ptr);
 			node = extent_tree_ad_search(&huge, &key);
 			assert(node != NULL);
 			assert(node->size == oldsize);
 			huge_allocated -= oldsize - psize;
 			/* No need to change huge_mapped, because we didn't
 			 * (un)map anything. */
 			node->size = psize;
 			malloc_mutex_unlock(&huge_mtx);
@@ -4423,17 +4416,17 @@ huge_ralloc(void *ptr, size_t size, size
                  * do need to update the recorded size if the size increased,
                  * so malloc_usable_size doesn't return a value smaller than
                  * what was requested via realloc(). */
 
                 if (psize > oldsize) {
                         /* Update recorded size. */
                         extent_node_t *node, key;
                         malloc_mutex_lock(&huge_mtx);
-                        key.addr = __DECONST(void *, ptr);
+                        key.addr = const_cast<void*>(ptr);
                         node = extent_tree_ad_search(&huge, &key);
                         assert(node != NULL);
                         assert(node->size == oldsize);
                         huge_allocated += psize - oldsize;
 			/* No need to change huge_mapped, because we didn't
 			 * (un)map anything. */
                         node->size = psize;
                         malloc_mutex_unlock(&huge_mtx);