diff -up firefox-52.6.0esr/js/src/vm/Runtime.cpp.disable-extra-threads firefox-52.6.0esr/js/src/vm/Runtime.cpp

--- firefox-52.6.0esr/js/src/vm/Runtime.cpp.disable-extra-threads	2018-02-08 10:16:13.453828939 -0500

+++ firefox-52.6.0esr/js/src/vm/Runtime.cpp	2018-02-08 10:23:31.283458826 -0500

@@ -283,6 +283,17 @@ JSRuntime::init(uint32_t maxbytes, uint3

     ownerThreadNative_ = (size_t)pthread_self();

 #endif

+    const char* enable_js_helper_threads;

+    enable_js_helper_threads = getenv("GJS_ENABLE_JS_HELPER_THREADS");

+

+#if defined(__PPC64__) && defined (__LITTLE_ENDIAN__)

+    if (enable_js_helper_threads == NULL)

+        js::DisableExtraThreads();

+#endif

+

+    if (enable_js_helper_threads != NULL && enable_js_helper_threads[0] == '0')

+        js::DisableExtraThreads();

+

     if (!mainThread.init())

         return false;