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)