--- firefox-66.0.5/js/src/jit/x86-shared/Assembler-x86-shared.cpp.orig	2019-05-11 23:41:10.894664764 +0100
+++ firefox-66.0.5/js/src/jit/x86-shared/Assembler-x86-shared.cpp	2019-05-12 11:39:51.269766814 +0100
@@ -328,12 +328,14 @@
     avxPresent = (xcr0EAX & xcr0SSEBit) && (xcr0EAX & xcr0AVXBit);
   }
 
+ if (maxSSEVersion >= SSE2) {
   // CMOV instruction are supposed to be supported by all CPU which have SSE2
   // enabled. While this might be true, this is not guaranteed by any
   // documentation, nor AMD, nor Intel.
   static constexpr int CMOVBit = 1 << 15;
   MOZ_RELEASE_ASSERT(flagsEdx & CMOVBit,
                      "CMOVcc instruction is not recognized by this CPU.");
+ }
 
   static constexpr int POPCNTBit = 1 << 23;
   popcntPresent = (flagsEcx & POPCNTBit);