--- old-configure.in.orig	2018-09-19 15:00:20.660000000 +0200
+++ old-configure.in	2018-09-19 15:04:32.850000000 +0200
@@ -722,12 +722,12 @@
 
 *-darwin*)
     HOST_CFLAGS="$HOST_CFLAGS -DXP_UNIX -DXP_MACOSX"
-    HOST_OPTIMIZE_FLAGS="${HOST_OPTIMIZE_FLAGS=-O3}"
+    HOST_OPTIMIZE_FLAGS="${HOST_OPTIMIZE_FLAGS=-O2}"
     ;;
 
 *-linux*|*-kfreebsd*-gnu|*-gnu*)
     HOST_CFLAGS="$HOST_CFLAGS -DXP_UNIX"
-    HOST_OPTIMIZE_FLAGS="${HOST_OPTIMIZE_FLAGS=-O3}"
+    HOST_OPTIMIZE_FLAGS="${HOST_OPTIMIZE_FLAGS=-O2}"
     ;;
 
 *)
@@ -758,7 +758,7 @@
 *-darwin*)
     MKSHLIB='$(CXX) $(COMPUTED_CXX_LDFLAGS) $(PGO_CFLAGS) $(DSO_PIC_CFLAGS) $(DSO_LDOPTS) -o $@'
     MKCSHLIB='$(CC) $(COMPUTED_C_LDFLAGS) $(PGO_CFLAGS) $(DSO_PIC_CFLAGS) $(DSO_LDOPTS) -o $@'
-    MOZ_OPTIMIZE_FLAGS="-O3"
+    MOZ_OPTIMIZE_FLAGS=""
     CXXFLAGS="$CXXFLAGS -stdlib=libc++"
     DSO_LDOPTS=''
     STRIP_FLAGS="$STRIP_FLAGS -x -S"
@@ -828,7 +828,7 @@
 
 *-*linux*)
     if test "$GNU_CC" -o "$GNU_CXX"; then
-        MOZ_PGO_OPTIMIZE_FLAGS="-O3"
+        MOZ_PGO_OPTIMIZE_FLAGS="-O2"
         if test -n "$MOZ_DEBUG"; then
             MOZ_OPTIMIZE_FLAGS="-Os"
         else
--- js/src/old-configure.in.orig	2018-09-19 15:05:33.330000000 +0200
+++ js/src/old-configure.in	2018-09-19 15:05:53.470000000 +0200
@@ -530,12 +530,12 @@
 
 *-darwin*)
     HOST_CFLAGS="$HOST_CFLAGS -DXP_UNIX -DXP_MACOSX"
-    HOST_OPTIMIZE_FLAGS="${HOST_OPTIMIZE_FLAGS=-O3}"
+    HOST_OPTIMIZE_FLAGS="${HOST_OPTIMIZE_FLAGS=-O2}"
     ;;
 
 *-linux*|*-kfreebsd*-gnu|*-gnu*)
     HOST_CFLAGS="$HOST_CFLAGS -DXP_UNIX"
-    HOST_OPTIMIZE_FLAGS="${HOST_OPTIMIZE_FLAGS=-O3}"
+    HOST_OPTIMIZE_FLAGS="${HOST_OPTIMIZE_FLAGS=-O2}"
     ;;
 
 *)
@@ -562,7 +562,7 @@
 *-darwin*)
     MKSHLIB='$(CXX) $(COMPUTED_CXX_LDFLAGS) $(PGO_CFLAGS) $(DSO_PIC_CFLAGS) $(DSO_LDOPTS) -o $@'
     MKCSHLIB='$(CC) $(COMPUTED_C_LDFLAGS) $(PGO_CFLAGS) $(DSO_PIC_CFLAGS) $(DSO_LDOPTS) -o $@'
-    MOZ_OPTIMIZE_FLAGS="-O3 -fno-stack-protector"
+    MOZ_OPTIMIZE_FLAGS="-O2 -fno-stack-protector"
     CFLAGS="$CFLAGS -fno-common"
     CXXFLAGS="$CXXFLAGS -fno-common -stdlib=libc++"
     DSO_LDOPTS=''
@@ -610,7 +610,7 @@
 *-android*|*-linuxandroid*)
     AC_DEFINE(NO_PW_GECOS)
     MOZ_GFX_OPTIMIZE_MOBILE=1
-    MOZ_OPTIMIZE_FLAGS="-O3"
+    MOZ_OPTIMIZE_FLAGS="-O2"
     if test -z "$CLANG_CC"; then
        MOZ_OPTIMIZE_FLAGS="-freorder-blocks -fno-reorder-functions $MOZ_OPTIMIZE_FLAGS"
     fi
@@ -618,8 +618,8 @@
 
 *-*linux*)
     if test "$GNU_CC" -o "$GNU_CXX"; then
-        MOZ_PGO_OPTIMIZE_FLAGS="-O3"
-        MOZ_OPTIMIZE_FLAGS="-O3"
+        MOZ_PGO_OPTIMIZE_FLAGS="-O2"
+        MOZ_OPTIMIZE_FLAGS="-O2"
         if test -z "$CLANG_CC"; then
            MOZ_OPTIMIZE_FLAGS="-freorder-blocks $MOZ_OPTIMIZE_FLAGS"
         fi