diff --git a/netwerk/base/src/DashboardTypes.h b/netwerk/base/src/DashboardTypes.h
index 5d534943926..4e3de2ee558 100644
--- a/netwerk/base/src/DashboardTypes.h
+++ b/netwerk/base/src/DashboardTypes.h
@@ -2,8 +2,8 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-#ifndef nsDashboardTypes__
-#define nsDashboardTypes__
+#ifndef mozilla_net_DashboardTypes_h_
+#define mozilla_net_DashboardTypes_h_
 
 namespace mozilla {
 namespace net {
@@ -22,7 +22,7 @@ struct DNSCacheEntries
 {
     nsCString hostname;
     nsTArray<nsCString> hostaddr;
-    int8_t family;
+    uint16_t family;
     int64_t expiration;
 };
 
@@ -45,4 +45,4 @@ struct HttpRetParams
 
 } }
 
-#endif // nsDashboardTypes__
+#endif // mozilla_net_DashboardTypes_h_
diff --git a/netwerk/base/src/Makefile.in b/netwerk/base/src/Makefile.in
index e409aacf5eb..71ae73c4927 100644
--- a/netwerk/base/src/Makefile.in
+++ b/netwerk/base/src/Makefile.in
@@ -14,9 +14,7 @@ include $(DEPTH)/config/autoconf.mk
 MODULE		= necko
 LIBRARY_NAME	= neckobase_s
 LIBXUL_LIBRARY  = 1
-ifndef _MSC_VER
 FAIL_ON_WARNINGS := 1
-endif # !_MSC_VER
 
 EXPORTS = \
 		nsMIMEInputStream.h \
diff --git a/netwerk/base/src/nsSocketTransport2.cpp b/netwerk/base/src/nsSocketTransport2.cpp
index 7dd872ad19c..dfa52298e17 100644
--- a/netwerk/base/src/nsSocketTransport2.cpp
+++ b/netwerk/base/src/nsSocketTransport2.cpp
@@ -8,6 +8,7 @@
 #endif
 
 #include "nsSocketTransport2.h"
+#include "base/compiler_specific.h"
 #include "nsAtomicRefcnt.h"
 #include "nsIOService.h"
 #include "nsStreamUtils.h"
@@ -696,8 +697,8 @@ nsSocketTransport::nsSocketTransport()
     , mFD(nullptr)
     , mFDref(0)
     , mFDconnected(false)
-    , mInput(this)
-    , mOutput(this)
+    , ALLOW_THIS_IN_INITIALIZER_LIST(mInput(this))
+    , ALLOW_THIS_IN_INITIALIZER_LIST(mOutput(this))
     , mQoSBits(0x00)
 {
     SOCKET_LOG(("creating nsSocketTransport @%x\n", this));
diff --git a/netwerk/base/src/nsSocketTransportService2.cpp b/netwerk/base/src/nsSocketTransportService2.cpp
index 0c9c3669bd3..348d82258d8 100644
--- a/netwerk/base/src/nsSocketTransportService2.cpp
+++ b/netwerk/base/src/nsSocketTransportService2.cpp
@@ -630,7 +630,7 @@ nsSocketTransportService::Run()
     threadInt->SetObserver(this);
 
     // make sure the pseudo random number generator is seeded on this thread
-    srand(PR_Now());
+    srand(static_cast<unsigned>(PR_Now()));
 
     for (;;) {
         bool pendingEvents = false;
diff --git a/netwerk/base/src/nsStandardURL.cpp b/netwerk/base/src/nsStandardURL.cpp
index 5d682681c8b..438e6f1af95 100644
--- a/netwerk/base/src/nsStandardURL.cpp
+++ b/netwerk/base/src/nsStandardURL.cpp
@@ -1530,7 +1530,7 @@ nsStandardURL::SetPort(int32_t port)
 
         // need to remove the port number from the URL spec
         uint32_t start = mHost.mPos + mHost.mLen;
-        uint32_t lengthToCut = mPath.mPos - start;
+        int32_t lengthToCut = mPath.mPos - start;
         mSpec.Cut(start, lengthToCut);
         mAuthority.mLen -= lengthToCut;
         ShiftFromPath(-lengthToCut);
diff --git a/netwerk/base/src/nsStreamTransportService.cpp b/netwerk/base/src/nsStreamTransportService.cpp
index 4c43318ba2a..817aed84b74 100644
--- a/netwerk/base/src/nsStreamTransportService.cpp
+++ b/netwerk/base/src/nsStreamTransportService.cpp
@@ -186,14 +186,14 @@ nsInputStreamTransport::Read(char *buf, uint32_t count, uint32_t *result)
     }
 
     // limit amount read
-    uint32_t max = mLimit - mOffset;
+    uint64_t max = mLimit - mOffset;
     if (max == 0) {
         *result = 0;
         return NS_OK;
     }
-        
+
     if (count > max)
-        count = max;
+        count = static_cast<uint32_t>(max);
 
     nsresult rv = mSource->Read(buf, count, result);
 
@@ -386,14 +386,14 @@ nsOutputStreamTransport::Write(const char *buf, uint32_t count, uint32_t *result
     }
 
     // limit amount written
-    uint32_t max = mLimit - mOffset;
+    uint64_t max = mLimit - mOffset;
     if (max == 0) {
         *result = 0;
         return NS_OK;
     }
-        
+
     if (count > max)
-        count = max;
+        count = static_cast<uint32_t>(max);
 
     nsresult rv = mSink->Write(buf, count, result);
 
diff --git a/netwerk/build/Makefile.in b/netwerk/build/Makefile.in
index ffe29b4f78a..d277c901892 100644
--- a/netwerk/build/Makefile.in
+++ b/netwerk/build/Makefile.in
@@ -17,9 +17,7 @@ IS_COMPONENT   = 1
 MODULE_NAME    = necko
 GRE_MODULE     = 1
 LIBXUL_LIBRARY = 1
-ifndef _MSC_VER
 FAIL_ON_WARNINGS := 1
-endif # !_MSC_VER
 
 CPPSRCS = nsNetModule.cpp
 EXPORTS = nsNetCID.h
diff --git a/netwerk/cache/Makefile.in b/netwerk/cache/Makefile.in
index 3457b40eef1..94ff3d8848f 100644
--- a/netwerk/cache/Makefile.in
+++ b/netwerk/cache/Makefile.in
@@ -15,9 +15,7 @@ LIBRARY_NAME   = nkcache_s
 LIBXUL_LIBRARY = 1
 XPIDL_MODULE   = necko_cache
 GRE_MODULE     = 1
-ifndef _MSC_VER
 FAIL_ON_WARNINGS := 1
-endif # !_MSC_VER
 
 FORCE_STATIC_LIB = 1
 
diff --git a/netwerk/cache/nsCacheService.cpp b/netwerk/cache/nsCacheService.cpp
index 20d6ec8dd71..83032eda8dc 100644
--- a/netwerk/cache/nsCacheService.cpp
+++ b/netwerk/cache/nsCacheService.cpp
@@ -575,17 +575,17 @@ SmartCacheSize(const uint32_t availKB, bool shouldUseOldMaxSmartSize)
 
     // .5% of space above 25 GB
     if (avail10MBs > 2500) {
-        sz10MBs += (avail10MBs - 2500)*.005;
+        sz10MBs += static_cast<uint32_t>((avail10MBs - 2500)*.005);
         avail10MBs = 2500;
     }
     // 1% of space between 7GB -> 25 GB
     if (avail10MBs > 700) {
-        sz10MBs += (avail10MBs - 700)*.01;
+        sz10MBs += static_cast<uint32_t>((avail10MBs - 700)*.01);
         avail10MBs = 700;
     }
     // 5% of space between 500 MB -> 7 GB
     if (avail10MBs > 50) {
-        sz10MBs += (avail10MBs - 50)*.05;
+        sz10MBs += static_cast<uint32_t>((avail10MBs - 50)*.05);
         avail10MBs = 50;
     }
 
@@ -595,10 +595,10 @@ SmartCacheSize(const uint32_t availKB, bool shouldUseOldMaxSmartSize)
     // percentage of available space and a smaller minimum.
 
     // 20% of space up to 500 MB (10 MB min)
-    sz10MBs += std::max<uint32_t>(1, avail10MBs * .2);
+    sz10MBs += std::max<uint32_t>(1, static_cast<uint32_t>(avail10MBs * .2));
 #else
     // 40% of space up to 500 MB (50 MB min)
-    sz10MBs += std::max<uint32_t>(5, avail10MBs * .4);
+    sz10MBs += std::max<uint32_t>(5, static_cast<uint32_t>(avail10MBs * .4));
 #endif
 
     return std::min<uint32_t>(maxSize, sz10MBs * 10 * 1024);
@@ -634,7 +634,8 @@ nsCacheProfilePrefObserver::GetSmartCacheSize(const nsAString& cachePath,
     if (NS_FAILED(rv))
         return DEFAULT_CACHE_SIZE;
 
-    return SmartCacheSize((bytesAvailable / 1024) + currentSize,
+    return SmartCacheSize(static_cast<uint32_t>((bytesAvailable / 1024) +
+                                                currentSize),
                           shouldUseOldMaxSmartSize);
 }
 
diff --git a/netwerk/cache/nsDeleteDir.cpp b/netwerk/cache/nsDeleteDir.cpp
index b4ef844e1f8..248cce07fc0 100644
--- a/netwerk/cache/nsDeleteDir.cpp
+++ b/netwerk/cache/nsDeleteDir.cpp
@@ -224,7 +224,7 @@ nsDeleteDir::DeleteDir(nsIFile *dirIn, bool moveToTrash, uint32_t delay)
       return rv;
 
     // Append random number to the trash directory and check if it exists.
-    srand(PR_Now());
+    srand(static_cast<unsigned>(PR_Now()));
     nsAutoCString leaf;
     for (int32_t i = 0; i < 10; i++) {
       leaf = origLeaf;
diff --git a/netwerk/cookie/Makefile.in b/netwerk/cookie/Makefile.in
index c3f1151b99e..452f2b0fd92 100644
--- a/netwerk/cookie/Makefile.in
+++ b/netwerk/cookie/Makefile.in
@@ -15,9 +15,7 @@ include $(DEPTH)/config/autoconf.mk
 MODULE       = necko
 XPIDL_MODULE = necko_cookie
 GRE_MODULE   = 1
-ifndef _MSC_VER
 FAIL_ON_WARNINGS := 1
-endif # !_MSC_VER
 
 SDK_XPIDLSRCS = \
   nsICookie.idl \
diff --git a/netwerk/cookie/nsCookieService.cpp b/netwerk/cookie/nsCookieService.cpp
index 7cc2f3b7cf4..093886b17b9 100644
--- a/netwerk/cookie/nsCookieService.cpp
+++ b/netwerk/cookie/nsCookieService.cpp
@@ -85,7 +85,7 @@ static const char kOldCookieFileName[] = "cookies.txt";
 #define LIMIT(x, low, high, default) ((x) >= (low) && (x) <= (high) ? (x) : (default))
 
 #undef  ADD_TEN_PERCENT
-#define ADD_TEN_PERCENT(i) ((i) + (i)/10)
+#define ADD_TEN_PERCENT(i) static_cast<uint32_t>((i) + (i)/10)
 
 // default limits for the cookie list. these can be tuned by the
 // network.cookie.maxNumber and network.cookie.maxPerHost prefs respectively.
diff --git a/netwerk/dns/Makefile.in b/netwerk/dns/Makefile.in
index f535587a906..3ed37a0957a 100644
--- a/netwerk/dns/Makefile.in
+++ b/netwerk/dns/Makefile.in
@@ -15,9 +15,7 @@ LIBRARY_NAME   = neckodns_s
 LIBXUL_LIBRARY = 1
 XPIDL_MODULE   = necko_dns
 GRE_MODULE     = 1
-ifndef _MSC_VER
 FAIL_ON_WARNINGS := 1
-endif # !_MSC_VER
 
 XPIDLSRCS = \
   nsIDNSListener.idl \
diff --git a/netwerk/protocol/http/Makefile.in b/netwerk/protocol/http/Makefile.in
index 597966a8c0f..12532d18cda 100644
--- a/netwerk/protocol/http/Makefile.in
+++ b/netwerk/protocol/http/Makefile.in
@@ -16,9 +16,7 @@ LIBXUL_LIBRARY = 1
 XPIDL_MODULE   = necko_http
 GRE_MODULE     = 1
 FORCE_STATIC_LIB = 1
-ifndef _MSC_VER
 FAIL_ON_WARNINGS := 1
-endif # !_MSC_VER
 
 EXPORTS_NAMESPACES = mozilla/net
 
diff --git a/netwerk/protocol/http/nsHttpAuthCache.cpp b/netwerk/protocol/http/nsHttpAuthCache.cpp
index 0109f8238ed..0a384ce8022 100644
--- a/netwerk/protocol/http/nsHttpAuthCache.cpp
+++ b/netwerk/protocol/http/nsHttpAuthCache.cpp
@@ -3,9 +3,10 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-#include <stdlib.h>
-#include "nsHttp.h"
 #include "nsHttpAuthCache.h"
+#include <stdlib.h>
+#include "base/compiler_specific.h"
+#include "nsHttp.h"
 #include "nsString.h"
 #include "nsCRT.h"
 #include "prprf.h"
@@ -50,7 +51,7 @@ StrEquivalent(const PRUnichar *a, const PRUnichar *b)
 
 nsHttpAuthCache::nsHttpAuthCache()
     : mDB(nullptr)
-    , mObserver(new AppDataClearObserver(this))
+    , ALLOW_THIS_IN_INITIALIZER_LIST(mObserver(new AppDataClearObserver(this)))
 {
     nsCOMPtr<nsIObserverService> obsSvc = mozilla::services::GetObserverService();
     if (obsSvc) {
diff --git a/netwerk/protocol/http/nsHttpConnectionMgr.cpp b/netwerk/protocol/http/nsHttpConnectionMgr.cpp
index f73d38c4f6b..b3017ecee12 100644
--- a/netwerk/protocol/http/nsHttpConnectionMgr.cpp
+++ b/netwerk/protocol/http/nsHttpConnectionMgr.cpp
@@ -2785,7 +2785,8 @@ nsHalfOpenSocket::OnOutputStreamReady(nsIAsyncOutputStream *out)
                         gHttpHandler->ConnMgr()->mMaxRequestDelay,
                         mSocketTransport, mStreamIn, mStreamOut,
                         callbacks,
-                        PR_MillisecondsToInterval(rtt.ToMilliseconds()));
+                        PR_MillisecondsToInterval(
+                          static_cast<uint32_t>(rtt.ToMilliseconds())));
 
         if (NS_SUCCEEDED(mSocketTransport->GetPeerAddr(&peeraddr)))
             mEnt->RecordIPFamilyPreference(peeraddr.raw.family);
@@ -2801,7 +2802,8 @@ nsHalfOpenSocket::OnOutputStreamReady(nsIAsyncOutputStream *out)
                         gHttpHandler->ConnMgr()->mMaxRequestDelay,
                         mBackupTransport, mBackupStreamIn, mBackupStreamOut,
                         callbacks,
-                        PR_MillisecondsToInterval(rtt.ToMilliseconds()));
+                        PR_MillisecondsToInterval(
+                          static_cast<uint32_t>(rtt.ToMilliseconds())));
 
         if (NS_SUCCEEDED(mBackupTransport->GetPeerAddr(&peeraddr)))
             mEnt->RecordIPFamilyPreference(peeraddr.raw.family);
diff --git a/netwerk/protocol/res/Makefile.in b/netwerk/protocol/res/Makefile.in
index 19fbded3392..ff9ee09ecce 100644
--- a/netwerk/protocol/res/Makefile.in
+++ b/netwerk/protocol/res/Makefile.in
@@ -15,9 +15,7 @@ LIBRARY_NAME   = nkres_s
 LIBXUL_LIBRARY = 1
 XPIDL_MODULE   = necko_res
 GRE_MODULE     = 1
-ifndef _MSC_VER
 FAIL_ON_WARNINGS = 1
-endif # !_MSC_VER
 
 FORCE_STATIC_LIB = 1
 
diff --git a/netwerk/protocol/websocket/Makefile.in b/netwerk/protocol/websocket/Makefile.in
index 39187fd71bb..42b90f532f0 100644
--- a/netwerk/protocol/websocket/Makefile.in
+++ b/netwerk/protocol/websocket/Makefile.in
@@ -15,9 +15,7 @@ LIBXUL_LIBRARY = 1
 XPIDL_MODULE   = necko_websocket
 GRE_MODULE     = 1
 FORCE_STATIC_LIB = 1
-ifndef _MSC_VER
 FAIL_ON_WARNINGS = 1
-endif # !_MSC_VER
 
 EXPORTS_NAMESPACES = mozilla/net
 
diff --git a/netwerk/protocol/websocket/WebSocketChannel.cpp b/netwerk/protocol/websocket/WebSocketChannel.cpp
index f6b55c156b1..2a1deb9369a 100644
--- a/netwerk/protocol/websocket/WebSocketChannel.cpp
+++ b/netwerk/protocol/websocket/WebSocketChannel.cpp
@@ -125,7 +125,8 @@ public:
     mLastFailure = TimeStamp::Now();
     // We use a truncated exponential backoff as suggested by RFC 6455,
     // but multiply by 1.5 instead of 2 to be more gradual.
-    mNextDelay = std::min<double>(kWSReconnectMaxDelay, mNextDelay * 1.5);
+    mNextDelay = static_cast<uint32_t>(
+      std::min<double>(kWSReconnectMaxDelay, mNextDelay * 1.5));
     LOG(("WebSocket: FailedAgain: host=%s, port=%d: incremented delay to %lu",
          mAddress.get(), mPort, mNextDelay));
   }
@@ -1179,26 +1180,26 @@ WebSocketChannel::ProcessInput(uint8_t *buffer, uint32_t count)
   uint32_t totalAvail = avail;
 
   while (avail >= 2) {
-    int64_t payloadLength = mFramePtr[1] & 0x7F;
-    uint8_t finBit        = mFramePtr[0] & kFinalFragBit;
-    uint8_t rsvBits       = mFramePtr[0] & 0x70;
-    uint8_t maskBit       = mFramePtr[1] & kMaskBit;
-    uint8_t opcode        = mFramePtr[0] & 0x0F;
+    int64_t payloadLength64 = mFramePtr[1] & 0x7F;
+    uint8_t finBit  = mFramePtr[0] & kFinalFragBit;
+    uint8_t rsvBits = mFramePtr[0] & 0x70;
+    uint8_t maskBit = mFramePtr[1] & kMaskBit;
+    uint8_t opcode  = mFramePtr[0] & 0x0F;
 
     uint32_t framingLength = 2;
     if (maskBit)
       framingLength += 4;
 
-    if (payloadLength < 126) {
+    if (payloadLength64 < 126) {
       if (avail < framingLength)
         break;
-    } else if (payloadLength == 126) {
+    } else if (payloadLength64 == 126) {
       // 16 bit length field
       framingLength += 2;
       if (avail < framingLength)
         break;
 
-      payloadLength = mFramePtr[2] << 8 | mFramePtr[3];
+      payloadLength64 = mFramePtr[2] << 8 | mFramePtr[3];
     } else {
       // 64 bit length
       framingLength += 8;
@@ -1215,18 +1216,19 @@ WebSocketChannel::ProcessInput(uint8_t *buffer, uint32_t count)
       // copy this in case it is unaligned
       uint64_t tempLen;
       memcpy(&tempLen, mFramePtr + 2, 8);
-      payloadLength = PR_ntohll(tempLen);
+      payloadLength64 = PR_ntohll(tempLen);
     }
 
     payload = mFramePtr + framingLength;
     avail -= framingLength;
 
     LOG(("WebSocketChannel::ProcessInput: payload %lld avail %lu\n",
-         payloadLength, avail));
+         payloadLength64, avail));
 
-    if (payloadLength + mFragmentAccumulator > mMaxMessageSize) {
+    if (payloadLength64 + mFragmentAccumulator > mMaxMessageSize) {
       return NS_ERROR_FILE_TOO_BIG;
     }
+    uint32_t payloadLength = static_cast<uint32_t>(payloadLength64);
 
     if (avail < payloadLength)
       break;
@@ -1266,7 +1268,7 @@ WebSocketChannel::ProcessInput(uint8_t *buffer, uint32_t count)
         return NS_ERROR_ILLEGAL_VALUE;
       }
 
-      LOG(("WebSocketChannel:: Accumulating Fragment %lld\n", payloadLength));
+      LOG(("WebSocketChannel:: Accumulating Fragment %ld\n", payloadLength));
 
       if (opcode == kContinuation) {
 
@@ -1358,7 +1360,7 @@ WebSocketChannel::ProcessInput(uint8_t *buffer, uint32_t count)
           memcpy(&mServerCloseCode, payload, 2);
           mServerCloseCode = PR_ntohs(mServerCloseCode);
           LOG(("WebSocketChannel:: close recvd code %u\n", mServerCloseCode));
-          uint16_t msglen = payloadLength - 2;
+          uint16_t msglen = static_cast<uint16_t>(payloadLength - 2);
           if (msglen > 0) {
             mServerCloseReason.SetLength(msglen);
             memcpy(mServerCloseReason.BeginWriting(),
diff --git a/netwerk/protocol/websocket/WebSocketChannelChild.cpp b/netwerk/protocol/websocket/WebSocketChannelChild.cpp
index ce3470e82f0..e2b8e4fdf79 100644
--- a/netwerk/protocol/websocket/WebSocketChannelChild.cpp
+++ b/netwerk/protocol/websocket/WebSocketChannelChild.cpp
@@ -5,6 +5,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "WebSocketLog.h"
+#include "base/compiler_specific.h"
 #include "mozilla/dom/TabChild.h"
 #include "mozilla/net/NeckoChild.h"
 #include "WebSocketChannelChild.h"
@@ -48,7 +49,7 @@ NS_INTERFACE_MAP_BEGIN(WebSocketChannelChild)
 NS_INTERFACE_MAP_END
 
 WebSocketChannelChild::WebSocketChannelChild(bool aSecure)
-: mEventQ(static_cast<nsIWebSocketChannel*>(this))
+: ALLOW_THIS_IN_INITIALIZER_LIST(mEventQ(static_cast<nsIWebSocketChannel*>(this)))
 , mIPCOpen(false)
 {
   LOG(("WebSocketChannelChild::WebSocketChannelChild() %p\n", this));
diff --git a/netwerk/protocol/wyciwyg/Makefile.in b/netwerk/protocol/wyciwyg/Makefile.in
index 299989ced1e..2a9aafb19f6 100644
--- a/netwerk/protocol/wyciwyg/Makefile.in
+++ b/netwerk/protocol/wyciwyg/Makefile.in
@@ -15,9 +15,7 @@ LIBXUL_LIBRARY	= 1
 XPIDL_MODULE	= necko_wyciwyg
 GRE_MODULE	= 1
 FORCE_STATIC_LIB = 1
-ifndef _MSC_VER
 FAIL_ON_WARNINGS = 1
-endif # !_MSC_VER
 
 EXPORTS_NAMESPACES = mozilla/net
 
diff --git a/netwerk/protocol/wyciwyg/WyciwygChannelChild.cpp b/netwerk/protocol/wyciwyg/WyciwygChannelChild.cpp
index dba8fecc4b1..d9dc8e87ea9 100644
--- a/netwerk/protocol/wyciwyg/WyciwygChannelChild.cpp
+++ b/netwerk/protocol/wyciwyg/WyciwygChannelChild.cpp
@@ -4,6 +4,8 @@
 
 #include "nsWyciwyg.h"
 
+#include "base/compiler_specific.h"
+
 #include "mozilla/net/NeckoChild.h"
 #include "WyciwygChannelChild.h"
 #include "mozilla/dom/TabChild.h"
@@ -39,7 +41,7 @@ WyciwygChannelChild::WyciwygChannelChild()
   , mState(WCC_NEW)
   , mIPCOpen(false)
   , mSentAppData(false)
-  , mEventQ(NS_ISUPPORTS_CAST(nsIWyciwygChannel*, this))
+  , ALLOW_THIS_IN_INITIALIZER_LIST(mEventQ(NS_ISUPPORTS_CAST(nsIWyciwygChannel*, this)))
 {
   LOG(("Creating WyciwygChannelChild @%x\n", this));
 }
diff --git a/netwerk/streamconv/converters/Makefile.in b/netwerk/streamconv/converters/Makefile.in
index 587b77c0085..a2f7330217f 100644
--- a/netwerk/streamconv/converters/Makefile.in
+++ b/netwerk/streamconv/converters/Makefile.in
@@ -13,9 +13,7 @@ include $(DEPTH)/config/autoconf.mk
 MODULE		= necko
 LIBRARY_NAME	= nkcnvts_s
 LIBXUL_LIBRARY = 1
-ifndef _MSC_VER
 FAIL_ON_WARNINGS := 1
-endif # !_MSC_VER
 
 
 CPPSRCS		= \
diff --git a/netwerk/streamconv/converters/nsMultiMixedConv.cpp b/netwerk/streamconv/converters/nsMultiMixedConv.cpp
index 9811c3fb12e..024c057ce04 100644
--- a/netwerk/streamconv/converters/nsMultiMixedConv.cpp
+++ b/netwerk/streamconv/converters/nsMultiMixedConv.cpp
@@ -883,7 +883,7 @@ nsMultiMixedConv::SendData(char *aBuffer, uint32_t aLen) {
         // make sure that we don't send more than the mContentLength
         // XXX why? perhaps the Content-Length header was actually wrong!!
         if ((uint64_t(aLen) + mTotalSent) > mContentLength)
-            aLen = mContentLength - mTotalSent;
+            aLen = static_cast<uint32_t>(mContentLength - mTotalSent);
 
         if (aLen == 0)
             return NS_OK;