diff -up firefox-55.0.2/js/src/jit/AtomicOperations.h.jit-atomic-lucky firefox-55.0.2/js/src/jit/AtomicOperations.h
--- firefox-55.0.2/js/src/jit/AtomicOperations.h.jit-atomic-lucky	2017-07-31 18:20:47.000000000 +0200
+++ firefox-55.0.2/js/src/jit/AtomicOperations.h	2017-08-29 12:59:52.870926044 +0200
@@ -348,7 +348,7 @@ AtomicOperations::isLockfree(int32_t siz
 # elif defined(__sh__)
 #  include "jit/none/AtomicOperations-feeling-lucky.h"
 # else
-#  include "jit/none/AtomicOperations-none.h" // These MOZ_CRASH() always
+#  include "jit/none/AtomicOperations-feeling-lucky.h"
 # endif
 #elif defined(JS_CODEGEN_X86) || defined(JS_CODEGEN_X64)
 # include "jit/x86-shared/AtomicOperations-x86-shared.h"
diff -up firefox-55.0.2/js/src/jit/none/AtomicOperations-feeling-lucky.h.jit-atomic-lucky firefox-55.0.2/js/src/jit/none/AtomicOperations-feeling-lucky.h
--- firefox-55.0.2/js/src/jit/none/AtomicOperations-feeling-lucky.h.jit-atomic-lucky	2017-08-29 14:10:52.665031524 +0200
+++ firefox-55.0.2/js/src/jit/none/AtomicOperations-feeling-lucky.h	2017-08-29 14:09:40.756060235 +0200
@@ -60,6 +60,14 @@
 #  define GNUC_COMPATIBLE
 #endif
 
+#ifdef __s390__
+#  define GNUC_COMPATIBLE
+#endif
+
+#ifdef __s390x__
+#  define GNUC_COMPATIBLE
+#endif
+
 // The default implementation tactic for gcc/clang is to use the newer
 // __atomic intrinsics added for use in C++11 <atomic>.  Where that
 // isn't available, we use GCC's older __sync functions instead.