--- a/toolkit/system/osxproxy/ProxyUtils.mm
+++ b/toolkit/system/osxproxy/ProxyUtils.mm
@@ -1,20 +1,137 @@
 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * 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 "ProxyUtils.h"
+#include "nsTArray.h"
+#include "prnetdb.h"
+#include "prtypes.h"
 
 namespace mozilla {
 namespace toolkit {
 namespace system {
 
-bool IsHostProxyEntry(const nsACString& aHost, const nsACString& aOverride)
+/**
+ * Normalize the short IP form into the complete form.
+ * For example, it converts "192.168" into "192.168.0.0"
+ */
+static bool
+NormalizeAddr(const nsACString& aAddr, nsCString& aNormalized)
+{
+  nsTArray<nsCString> addr;
+  if (!ParseString(aAddr, '.', addr)) {
+    return false;
+  }
+  aNormalized = "";
+  for (uint32_t i = 0; i < 4; ++i) {
+    if (i != 0) {
+      aNormalized.Append(".");
+    }
+    if (i < addr.Length()) {
+      aNormalized.Append(addr[i]);
+    } else {
+      aNormalized.Append("0");
+    }
+  }
+  return true;
+}
+
+static PRUint32
+MaskIPv4Addr(PRUint32 aAddr, uint16_t aMaskLen)
+{
+  if (aMaskLen == 32) {
+    return aAddr;
+  }
+  return PR_htonl(PR_ntohl(aAddr) & (~0L << (32 - aMaskLen)));
+}
+
+static void
+MaskIPv6Addr(PRIPv6Addr& aAddr, uint16_t aMaskLen)
+{
+  if (aMaskLen == 128)
+    return;
+
+  if (aMaskLen > 96) {
+    aAddr.pr_s6_addr32[3] = PR_htonl(
+        PR_ntohl(aAddr.pr_s6_addr32[3]) & (~0L << (128 - aMaskLen)));
+  } else if (aMaskLen > 64) {
+    aAddr.pr_s6_addr32[3] = 0;
+    aAddr.pr_s6_addr32[2] = PR_htonl(
+        PR_ntohl(aAddr.pr_s6_addr32[2]) & (~0L << (96 - aMaskLen)));
+  } else if (aMaskLen > 32) {
+    aAddr.pr_s6_addr32[3] = 0;
+    aAddr.pr_s6_addr32[2] = 0;
+    aAddr.pr_s6_addr32[1] = PR_htonl(
+        PR_ntohl(aAddr.pr_s6_addr32[1]) & (~0L << (64 - aMaskLen)));
+  } else {
+    aAddr.pr_s6_addr32[3] = 0;
+    aAddr.pr_s6_addr32[2] = 0;
+    aAddr.pr_s6_addr32[1] = 0;
+    aAddr.pr_s6_addr32[0] = PR_htonl(
+        PR_ntohl(aAddr.pr_s6_addr32[0]) & (~0L << (32 - aMaskLen)));
+  }
+
+  return;
+}
+
+static bool
+IsMatchMask(const nsACString& aHost, const nsACString& aOverride)
+{
+  nsresult rv;
+
+  auto tokenEnd = aOverride.FindChar('/');
+  if (tokenEnd == -1) {
+    return false;
+  }
+
+  nsAutoCString prefixStr(Substring(aOverride,
+                                    tokenEnd + 1,
+                                    aOverride.Length() - tokenEnd - 1));
+  auto maskLen = prefixStr.ToInteger(&rv);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return false;
+  }
+
+  nsAutoCString override(aOverride);
+  if (!NormalizeAddr(Substring(aOverride, 0, tokenEnd), override)) {
+    return false;
+  }
+
+  PRNetAddr prAddrHost;
+  PRNetAddr prAddrOverride;
+  if (PR_SUCCESS != PR_StringToNetAddr(PromiseFlatCString(aHost).get(),
+                                       &prAddrHost) ||
+      PR_SUCCESS != PR_StringToNetAddr(override.get(),
+                                       &prAddrOverride)) {
+    return false;
+  }
+
+  if (prAddrHost.raw.family == PR_AF_INET &&
+      prAddrOverride.raw.family == PR_AF_INET) {
+    return MaskIPv4Addr(prAddrHost.inet.ip, maskLen) ==
+           MaskIPv4Addr(prAddrOverride.inet.ip, maskLen);
+  }
+  else if (prAddrHost.raw.family == PR_AF_INET6 &&
+      prAddrOverride.raw.family == PR_AF_INET6) {
+    MaskIPv6Addr(prAddrHost.ipv6.ip, maskLen);
+    MaskIPv6Addr(prAddrOverride.ipv6.ip, maskLen);
+
+    return memcmp(&prAddrHost.ipv6.ip,
+                  &prAddrOverride.ipv6.ip,
+                  sizeof(PRIPv6Addr)) == 0;
+  }
+
+  return false;
+}
+
+static bool
+IsMatchWildcard(const nsACString& aHost, const nsACString& aOverride)
 {
   nsAutoCString host(aHost);
   nsAutoCString override(aOverride);
 
   int32_t overrideLength = override.Length();
   int32_t tokenStart = 0;
   int32_t offset = 0;
   bool star = false;
@@ -40,11 +157,17 @@ bool IsHostProxyEntry(const nsACString& 
       tokenStart = tokenEnd;
       offset += token.Length();
     }
   }
 
   return (star || (offset == static_cast<int32_t>(host.Length())));
 }
 
+bool
+IsHostProxyEntry(const nsACString& aHost, const nsACString& aOverride)
+{
+  return IsMatchMask(aHost, aOverride) || IsMatchWildcard(aHost, aOverride);
+}
+
 } // namespace system
 } // namespace toolkit
 } // namespace mozilla