--- a/accessible/windows/msaa/moz.build
+++ b/accessible/windows/msaa/moz.build
@@ -68,8 +68,14 @@ if CONFIG['CLANG_CL']:
     CXXFLAGS += ['-Wno-extra-tokens']
 
 include('/ipc/chromium/chromium-config.mozbuild')
 
 FINAL_LIBRARY = 'xul'
 
 if CONFIG['GNU_CXX']:
     CXXFLAGS += ['-Wshadow']
+
+if CONFIG['_MSC_VER']:
+    # Intended as a temporary workaround to enable compilation on VS2015
+    # AccessibleWrap.cpp(1528): warning C4312: 'reinterpret_cast': conversion
+    # from 'const LONG' to 'void *' of greater size
+    CXXFLAGS += ['-wd4312']

--- a/accessible/xul/moz.build
+++ b/accessible/xul/moz.build
@@ -42,9 +42,14 @@ elif CONFIG['MOZ_WIDGET_TOOLKIT'] == 'co
     LOCAL_INCLUDES += [
         '/accessible/mac',
     ]
 else:
     LOCAL_INCLUDES += [
         '/accessible/other',
     ]
 
+if CONFIG['_MSC_VER']:
+    # This is intended as a temporary hack to support building with VS2015.
+    # 'reinterpret_cast': conversion from 'int32_t' to 'void *' of greater size
+    CXXFLAGS += ['-wd4312']
+
 FINAL_LIBRARY = 'xul'

--- a/dom/canvas/moz.build
+++ b/dom/canvas/moz.build
@@ -178,8 +178,13 @@ LOCAL_INCLUDES += [
     '/layout/xul',
     '/media/libyuv/include',
 ]
 
 CXXFLAGS += CONFIG['MOZ_CAIRO_CFLAGS']
 CXXFLAGS += CONFIG['TK_CFLAGS']
 
 LOCAL_INCLUDES += CONFIG['SKIA_INCLUDES']
+
+if CONFIG['_MSC_VER']:
+    # This is intended as a temporary workaround to unblock compilation
+    # on VS2015 in warnings as errors mode.
+    CXXFLAGS += ['-wd4312']

--- a/dom/media/moz.build
+++ b/dom/media/moz.build
@@ -319,9 +319,14 @@ if CONFIG['MOZ_GONK_MEDIACODEC']:
 include('/ipc/chromium/chromium-config.mozbuild')
 
 # Suppress some GCC warnings being treated as errors:
 #  - about attributes on forward declarations for types that are already
 #    defined, which complains about an important MOZ_EXPORT for android::AString
 if CONFIG['GNU_CC']:
   CXXFLAGS += ['-Wno-error=attributes']
 
+if CONFIG['_MSC_VER']:
+    # This is intended as a temporary workaround to unblock compilation
+    # on VS2015 in warnings as errors mode.
+    CXXFLAGS += ['-wd4312']
+
 FINAL_LIBRARY = 'xul'

--- a/dom/media/systemservices/moz.build
+++ b/dom/media/systemservices/moz.build
@@ -52,16 +52,21 @@ if CONFIG['MOZ_WIDGET_TOOLKIT'] == 'gonk
     else:
         LOCAL_INCLUDES += [
             '%' + '%s/system/media/wilhelm/include' % CONFIG['ANDROID_SOURCE'],
         ]
 
 if CONFIG['_MSC_VER']:
     DEFINES['__PRETTY_FUNCTION__'] = '__FUNCSIG__'
 
+    # This is intended as a temporary workaround to enable building with VS2015.
+    # media\webrtc\trunk\webrtc/base/criticalsection.h(59): warning C4312:
+    # 'reinterpret_cast': conversion from 'DWORD' to 'HANDLE' of greater size
+    CXXFLAGS += ['-wd4312']
+
 EXPORTS.mozilla += ['ShmemPool.h',]
 
 EXPORTS.mozilla.media += ['MediaChild.h',
                           'MediaParent.h',
                           'MediaSystemResourceClient.h',
                           'MediaSystemResourceManager.h',
                           'MediaSystemResourceManagerChild.h',
                           'MediaSystemResourceManagerParent.h',

--- a/dom/plugins/ipc/moz.build
+++ b/dom/plugins/ipc/moz.build
@@ -147,8 +147,12 @@ else:
     CXXFLAGS += CONFIG['MOZ_GTK2_CFLAGS']
 
 CXXFLAGS += CONFIG['MOZ_CAIRO_CFLAGS']
 
 if CONFIG['_MSC_VER']:
     # This is intended as a temporary hack to support building with VS2015.
     # conversion from 'X' to 'Y' requires a narrowing conversion
     CXXFLAGS += ['-wd4838']
+
+    # 'type cast': conversion from 'unsigned int' to 'HIMC' of greater size
+    CXXFLAGS += ['-wd4312']
+

--- a/ipc/chromium/moz.build
+++ b/ipc/chromium/moz.build
@@ -167,8 +167,14 @@ if '86' not in ost and 'arm' not in ost 
         'src/base/atomicops_internals_mutex.cc',
     ]
 
 CXXFLAGS += CONFIG['TK_CFLAGS']
 
 include('/ipc/chromium/chromium-config.mozbuild')
 
 FINAL_LIBRARY = 'xul'
+
+if CONFIG['_MSC_VER']:
+    # This is intended as a temporary workaround to enable building with VS2015.
+    # src/base/thread_local.h(110): warning C4312: 'reinterpret_cast':
+    # conversion from 'int' to 'void *' of greater size
+    CXXFLAGS += ['-wd4312']

--- a/ipc/glue/moz.build
+++ b/ipc/glue/moz.build
@@ -131,16 +131,22 @@ SOURCES += [
     'BackgroundChildImpl.cpp',
     'BackgroundParentImpl.cpp',
     'FileDescriptorSetChild.cpp',
     'FileDescriptorSetParent.cpp',
     'GeckoChildProcessHost.cpp',
     'URIUtils.cpp',
 ]
 
+if CONFIG['_MSC_VER']:
+    # This is intended as a temporary hack to support building with VS2015.
+    # 'reinterpret_cast': conversion from 'DWORD' to 'HANDLE' of greater size
+    SOURCES['BackgroundChildImpl.cpp'].flags += ['-wd4312']
+    SOURCES['BackgroundParentImpl.cpp'].flags += ['-wd4312']
+
 LOCAL_INCLUDES += [
     '/caps',
     '/dom/broadcastchannel',
     '/dom/indexedDB',
     '/dom/workers',
     '/media/webrtc/trunk',
     '/xpcom/build',
 ]

--- a/js/src/gdb/moz.build
+++ b/js/src/gdb/moz.build
@@ -29,8 +29,11 @@ LOCAL_INCLUDES += [
     '..',
 ]
 
 USE_LIBS += [
     'static:js',
 ]
 
 OS_LIBS += CONFIG['MOZ_ZLIB_LIBS']
+
+if CONFIG['_MSC_VER']:
+    CXXFLAGS += ['-wd4312']
\ No newline at end of file

--- a/js/src/jsapi-tests/moz.build
+++ b/js/src/jsapi-tests/moz.build
@@ -119,8 +119,11 @@ LOCAL_INCLUDES += [
     '..',
 ]
 
 USE_LIBS += [
     'static:js',
 ]
 
 OS_LIBS += CONFIG['MOZ_ZLIB_LIBS']
+
+if CONFIG['_MSC_VER']:
+    CXXFLAGS += ['-wd4312']
\ No newline at end of file

--- a/js/src/moz.build
+++ b/js/src/moz.build
@@ -665,16 +665,18 @@ if CONFIG['_MSC_VER']:
     CXXFLAGS += ['-wd4146'] # FIXME: unary minus operator applied to unsigned type (bug 1229189)
     CXXFLAGS += ['-wd4273'] # FIXME: inconsistent dll linkage (bug 1229666)
 
     # This is intended as a temporary hack to support building with VS2015.
     # 'noexcept' used with no exception handling mode specified;
     # termination on exception is not guaranteed. Specify /EHsc
     CXXFLAGS += ['-wd4577']
 
+    CXXFLAGS += ['-wd4312']
+
 if CONFIG['OS_ARCH'] not in ('WINNT', 'HP-UX'):
     OS_LIBS += [
         'm',
     ]
 
 if CONFIG['OS_ARCH'] == 'FreeBSD':
     OS_LIBS += [
         '-pthread',

--- a/js/src/shell/moz.build
+++ b/js/src/shell/moz.build
@@ -39,8 +39,11 @@ OS_LIBS += CONFIG['MOZ_ZLIB_LIBS']
 # Prepare module loader JS code for embedding
 GENERATED_FILES += ['shellmoduleloader.out.h']
 shellmoduleloader = GENERATED_FILES['shellmoduleloader.out.h']
 shellmoduleloader.script = '../builtin/embedjs.py:generate_shellmoduleloader'
 shellmoduleloader.inputs = [
     '../js.msg',
     'ModuleLoader.js',
 ]
+
+if CONFIG['_MSC_VER']:
+    CXXFLAGS += ['-wd4312']
\ No newline at end of file

--- a/media/webrtc/moz.build
+++ b/media/webrtc/moz.build
@@ -88,16 +88,17 @@ if CONFIG['MOZ_WEBRTC_SIGNALING']:
         'signaling/src/sdp/sipcc/sdp_base64.c',
         'signaling/src/sdp/sipcc/sdp_config.c',
         'signaling/src/sdp/sipcc/sdp_main.c',
         'signaling/src/sdp/sipcc/sdp_services_unix.c',
         'signaling/src/sdp/sipcc/sdp_token.c',
         'signaling/src/sdp/sipcc/sdp_utils.c',
     ]
 
+    GYP_DIRS['signaling'].sandbox_vars['ALLOW_COMPILER_WARNINGS'] = True
     GYP_DIRS['signaling'].non_unified_sources += signaling_non_unified_sources
 
 if CONFIG['MOZ_WIDGET_TOOLKIT'] != 'gonk':
     GYP_DIRS += ['trunk/testing']
     GYP_DIRS['trunk/testing'].input = 'trunk/testing/gtest.gyp'
     GYP_DIRS['trunk/testing'].variables = gyp_vars
     # We allow warnings for third-party code that can be updated from upstream.
     GYP_DIRS['trunk/testing'].sandbox_vars['ALLOW_COMPILER_WARNINGS'] = True
@@ -107,9 +108,10 @@ if CONFIG['MOZ_WIDGET_TOOLKIT'] != 'gonk
         GYP_DIRS += ['signalingtest']
         GYP_DIRS['signalingtest'].input = 'signaling/signaling.gyp'
         GYP_DIRS['signalingtest'].variables = gyp_vars.copy()
         GYP_DIRS['signalingtest'].variables.update(
             build_for_test=1,
             moz_webrtc_mediacodec=0,
             build_for_standalone=0
         )
+        GYP_DIRS['signalingtest'].sandbox_vars['ALLOW_COMPILER_WARNINGS'] = True
         GYP_DIRS['signalingtest'].non_unified_sources += signaling_non_unified_sources

--- a/media/webrtc/signaling/test/moz.build
+++ b/media/webrtc/signaling/test/moz.build
@@ -19,8 +19,14 @@ if CONFIG['OS_TARGET'] != 'WINNT' and CO
 include('/ipc/chromium/chromium-config.mozbuild')
 include('common.build')
 
 USE_LIBS += [
     '/media/webrtc/signalingtest/signaling_ecc/ecc',
     'mtransport_s',
 ]
 
+if CONFIG['_MSC_VER']:
+    # This is intended as a temporary workaround to enable warning free building
+    # with VS2015.
+    # reinterpret_cast': conversion from 'DWORD' to 'HANDLE' of greater size
+    CXXFLAGS += ['-wd4312']
+

--- a/parser/html/moz.build
+++ b/parser/html/moz.build
@@ -95,8 +95,13 @@ FINAL_LIBRARY = 'xul'
 # DEFINES['ENABLE_VOID_MENUITEM'] = True
 
 LOCAL_INCLUDES += [
     '/dom/base',
 ]
 
 if CONFIG['CLANG_CXX']:
     CXXFLAGS += ['-Wno-implicit-fallthrough']
+
+if CONFIG['_MSC_VER']:
+    # This is intended as a temporary hack to support building with VS2015.
+    # 'type cast': conversion from 'unsigned int' to 'nsIContent *' of greater size
+    CXXFLAGS += ['-wd4312']

--- a/security/sandbox/staticruntime/moz.build
+++ b/security/sandbox/staticruntime/moz.build
@@ -28,10 +28,11 @@ if CONFIG['OS_ARCH'] == 'WINNT':
 
     # Suppress warnings in third-party code.
     if CONFIG['_MSC_VER']:
         CXXFLAGS += [
             '-wd4275', # non dll-interface class exception used as base for dll-interface class
             '-wd4717', # recursive on all control paths, function will cause runtime stack overflow
             '-wd4996', # 'GetVersionExW': was declared deprecated
             '-wd4302', # 'reinterpret_cast': truncation from 'LPCSTR' to 'WORD'
+            '-wd4311',
             '-wd4312', # 'reinterpret_cast': conversion from 'DWORD' to 'LPOVERLAPPED' of greater size
         ]

--- a/widget/windows/moz.build
+++ b/widget/windows/moz.build
@@ -105,8 +105,13 @@ for var in ('MOZ_ENABLE_D3D10_LAYER'):
 
 RESFILE = 'widget.res'
 
 CXXFLAGS += CONFIG['MOZ_CAIRO_CFLAGS']
 
 OS_LIBS += [
     'rpcrt4',
 ]
+
+if CONFIG['_MSC_VER']:
+    # This is intended as a temporary hack to support building with VS2015.
+    # 'reinterpret_cast': conversion from 'int' to 'HANDLE' of greater size
+    CXXFLAGS += ['-wd4312']