diff -up firefox-68.1.0/xpcom/threads/nsThread.cpp.old firefox-68.1.0/xpcom/threads/nsThread.cpp
--- firefox-68.1.0/xpcom/threads/nsThread.cpp.old	2019-09-20 12:17:35.481661390 +0200
+++ firefox-68.1.0/xpcom/threads/nsThread.cpp	2019-09-20 12:19:14.269180516 +0200
@@ -556,7 +556,8 @@ void nsThread::InitCommon() {
     // kernel report them as separate regions, even when they are adjacent to
     // heap memory. This allows us to accurately track the actual memory
     // consumption of our allocated stacks.
-    madvise(mStackBase, stackSize, MADV_NOHUGEPAGE);
+    // not supported on RHEL6
+    // madvise(mStackBase, stackSize, MADV_NOHUGEPAGE);
 
     pthread_attr_destroy(&attr);
 #elif defined(XP_WIN)