--- a/xpcom/build/nsWindowsDllInterceptor.h
+++ b/xpcom/build/nsWindowsDllInterceptor.h
@@ -463,16 +463,79 @@ protected:
   const static int kPageSize = 4096;
   const static int kHookSize = 128;
 
   HMODULE mModule;
   byteptr_t mHookPage;
   int mMaxHooks;
   int mCurHooks;
 
+  // rex bits
+  static const BYTE kMaskHighNibble = 0xF0;
+  static const BYTE kRexOpcode = 0x40;
+  static const BYTE kMaskRexW = 0x08;
+  static const BYTE kMaskRexR = 0x04;
+  static const BYTE kMaskRexX = 0x02;
+  static const BYTE kMaskRexB = 0x01;
+
+  // mod r/m bits
+  static const BYTE kRegFieldShift = 3;
+  static const BYTE kMaskMod = 0xC0;
+  static const BYTE kMaskReg = 0x38;
+  static const BYTE kMaskRm = 0x07;
+  static const BYTE kRmNeedSib = 0x04;
+  static const BYTE kModReg = 0xC0;
+  static const BYTE kModDisp32 = 0x80;
+  static const BYTE kModDisp8 = 0x40;
+  static const BYTE kModNoRegDisp = 0x00;
+  static const BYTE kRmNoRegDispDisp32 = 0x05;
+
+  // sib bits
+  static const BYTE kMaskSibScale = 0xC0;
+  static const BYTE kMaskSibIndex = 0x38;
+  static const BYTE kMaskSibBase = 0x07;
+  static const BYTE kSibBaseEbp = 0x05;
+
+  int CountModRmSib(const BYTE *aModRm, BYTE* aSubOpcode)
+  {
+    if (!aModRm) {
+      return -1;
+    }
+    int numBytes = 1; // Start with 1 for mod r/m byte itself
+    switch (*aModRm & kMaskMod) {
+      case kModReg:
+        return numBytes;
+      case kModDisp8:
+        numBytes += 1;
+        break;
+      case kModDisp32:
+        numBytes += 4;
+        break;
+      case kModNoRegDisp:
+        if ((*aModRm & kMaskRm) == kRmNoRegDispDisp32 ||
+            ((*aModRm & kMaskRm) == kRmNeedSib &&
+             (*(aModRm + 1) & kMaskSibBase) == kSibBaseEbp)) {
+          numBytes += 4;
+        }
+        break;
+      default:
+        // This should not be reachable
+        MOZ_ASSERT_UNREACHABLE("Impossible value for modr/m byte mod bits");
+        return -1;
+    }
+    if ((*aModRm & kMaskRm) == kRmNeedSib) {
+      // SIB byte
+      numBytes += 1;
+    }
+    if (aSubOpcode) {
+      *aSubOpcode = (*aModRm & kMaskReg) >> kRegFieldShift;
+    }
+    return numBytes;
+  }
+
 #if defined(_M_X64)
   // To patch for JMP and JE
 
   enum JumpType {
    Je,
    Jmp
   };
 
@@ -770,16 +833,27 @@ protected:
         // nop
         nBytes++;
       } else if (origBytes[nBytes] == 0xb8) {
         // MOV 0xB8: http://ref.x86asm.net/coder32.html#xB8
         nBytes += 5;
       } else if (origBytes[nBytes] == 0x33) {
         // xor r32, r/m32
         nBytes += 2;
+      } else if (origBytes[nBytes] == 0xf6) {
+        // test r/m8, imm8 (used by ntdll on Windows 10 x64)
+        // (no flags are affected by near jmp since there is no task switch,
+        // so it is ok for a jmp to be written immediately after a test)
+        BYTE subOpcode = 0;
+        int nModRmSibBytes = CountModRmSib(&origBytes[nBytes + 1], &subOpcode);
+        if (nModRmSibBytes < 0 || subOpcode != 0) {
+          // Unsupported
+          return;
+        }
+        nBytes += 2 + nModRmSibBytes;
       } else if (origBytes[nBytes] == 0xc3) {
         // ret
         nBytes++;
       } else if (origBytes[nBytes] == 0xcc) {
         // int 3
         nBytes++;
       } else if (origBytes[nBytes] == 0xe9) {
         // jmp 32bit offset