Index: thunderbird-52.0/mozilla/old-configure.in
===================================================================
--- thunderbird-52.0/mozilla/old-configure.in
+++ thunderbird-52.0/mozilla/old-configure.in	2017-04-12 12:18:22.274692588 -0400
@@ -820,7 +820,7 @@
 
 *-linux*|*-kfreebsd*-gnu|*-gnu*)
     HOST_CFLAGS="$HOST_CFLAGS -DXP_UNIX"
-    HOST_OPTIMIZE_FLAGS="${HOST_OPTIMIZE_FLAGS=-O3}"
+    HOST_OPTIMIZE_FLAGS="${HOST_OPTIMIZE_FLAGS=-O2}"
     ;;
 
 *)
@@ -4277,7 +4277,7 @@
 dnl = Enable code optimization. ON by default.
 dnl ========================================================
 if test -z "$MOZ_OPTIMIZE_FLAGS"; then
-    MOZ_OPTIMIZE_FLAGS="-O"
+    MOZ_OPTIMIZE_FLAGS=""
 fi
 
 MOZ_ARG_ENABLE_STRING(optimize,
Index: thunderbird-52.0/mozilla/intl/icu/source/runConfigureICU
===================================================================
--- thunderbird-52.0/mozilla/intl/icu/source/runConfigureICU
+++ thunderbird-52.0/mozilla/intl/icu/source/runConfigureICU	2017-04-12 12:21:04.840937914 -0400
@@ -239,16 +239,16 @@
         THE_COMP="the GNU C++"
         CC=gcc; export CC
         CXX=g++; export CXX
-        RELEASE_CFLAGS='-O3'
-        RELEASE_CXXFLAGS='-O3'
+        RELEASE_CFLAGS='-O2'
+        RELEASE_CXXFLAGS='-O2'
         DEBUG_CFLAGS='-g'
         DEBUG_CXXFLAGS='-g'
         ;;
     Linux*)
         THE_OS="Linux"
         THE_COMP="the clang or else GNU C++"
-        RELEASE_CFLAGS='-O3'
-        RELEASE_CXXFLAGS='-O3'
+        RELEASE_CFLAGS='-O2'
+        RELEASE_CXXFLAGS='-O2'
         DEBUG_CFLAGS='-g'
         DEBUG_CXXFLAGS='-g'
         ;;
@@ -382,7 +382,7 @@
     then
         case $CC in
             gcc|*/gcc|*-gcc-*|*/*-gcc-*)
-                RELEASE_CFLAGS=-O3
+                RELEASE_CFLAGS=-O2
                 ;;
         esac
     fi
@@ -394,7 +394,7 @@
     then
         case $CXX in
             g++|*/g++|*-g++-*|*/*-g++-*)
-                RELEASE_CXXFLAGS=-O3
+                RELEASE_CXXFLAGS=-O2
                 ;;
         esac
     fi
Index: thunderbird-52.0/mozilla/media/libopus/moz.build
===================================================================
--- thunderbird-52.0/mozilla/media/libopus/moz.build
+++ thunderbird-52.0/mozilla/media/libopus/moz.build	2017-04-12 12:27:04.131484069 -0400
@@ -96,10 +96,10 @@
     # -Os is significantly slower, enable -O3 unless optimization is disabled
     if CONFIG['MOZ_OPTIMIZE']:
         CFLAGS += [
-            '-O3',
+            '-O2',
         ]
         CXXFLAGS += [
-            '-O3',
+            '-O2',
         ]
     # These flags are a lie; they're just used to enable the requisite
     # opcodes; actual arch detection is done at runtime.
Index: thunderbird-52.0/mozilla/memory/jemalloc/src/configure.ac
===================================================================
--- thunderbird-52.0/mozilla/memory/jemalloc/src/configure.ac
+++ thunderbird-52.0/mozilla/memory/jemalloc/src/configure.ac	2017-04-12 12:29:20.131690910 -0400
@@ -823,7 +823,7 @@
   echo "$CFLAGS $EXTRA_CFLAGS" | grep '\-O' >/dev/null || optimize="yes"
   if test "x${optimize}" = "xyes" ; then
     if test "x$GCC" = "xyes" ; then
-      JE_CFLAGS_APPEND([-O3])
+      JE_CFLAGS_APPEND([-O2])
       JE_CFLAGS_APPEND([-funroll-loops])
     elif test "x$je_cv_msvc" = "xyes" ; then
       JE_CFLAGS_APPEND([-O2])
Index: thunderbird-52.0/mozilla/config/moz.build
===================================================================
--- thunderbird-52.0/mozilla/config/moz.build
+++ thunderbird-52.0/mozilla/config/moz.build	2017-04-12 12:16:50.179553608 -0400
@@ -41,7 +41,7 @@
 ]
 
 if CONFIG['GNU_CC'] and CONFIG['MOZ_OPTIMIZE']:
-    CFLAGS += ['-O3']
+    CFLAGS += ['-O2']
 
 HOST_DEFINES = {
     'UNICODE': True,
Index: thunderbird-52.0/mozilla/js/src/old-configure.in
===================================================================
--- thunderbird-52.0/mozilla/js/src/old-configure.in
+++ thunderbird-52.0/mozilla/js/src/old-configure.in	2017-04-12 12:23:24.662150278 -0400
@@ -583,7 +583,7 @@
 
 *-linux*|*-kfreebsd*-gnu|*-gnu*)
     HOST_CFLAGS="$HOST_CFLAGS -DXP_UNIX"
-    HOST_OPTIMIZE_FLAGS="${HOST_OPTIMIZE_FLAGS=-O3}"
+    HOST_OPTIMIZE_FLAGS="${HOST_OPTIMIZE_FLAGS=-O2}"
     ;;
 
 *)
@@ -660,7 +660,7 @@
 *-*linux*)
     if test "$GNU_CC" -o "$GNU_CXX"; then
         MOZ_PGO_OPTIMIZE_FLAGS="-O3"
-        MOZ_OPTIMIZE_FLAGS="-O3"
+        MOZ_OPTIMIZE_FLAGS="-O2"
         if test -z "$CLANG_CC"; then
            MOZ_OPTIMIZE_FLAGS="-freorder-blocks $MOZ_OPTIMIZE_FLAGS"
         fi
@@ -1557,7 +1557,7 @@
 dnl = Enable code optimization. ON by default.
 dnl ========================================================
 if test -z "$MOZ_OPTIMIZE_FLAGS"; then
-	MOZ_OPTIMIZE_FLAGS="-O"
+	MOZ_OPTIMIZE_FLAGS=""
 fi
 
 MOZ_ARG_ENABLE_STRING(optimize,
Index: thunderbird-52.0/mozilla/js/src/ctypes/libffi/configure
===================================================================
--- thunderbird-52.0/mozilla/js/src/ctypes/libffi/configure
+++ thunderbird-52.0/mozilla/js/src/ctypes/libffi/configure	2017-04-12 12:25:18.765323818 -0400
@@ -16193,7 +16193,7 @@
 
     gnu)
      # default optimization flags for gcc on all systems
-     CFLAGS="-O3 -fomit-frame-pointer"
+     CFLAGS="-O2"
 
      # -malign-double for x86 systems
      # LIBFFI -- DON'T DO THIS - CHANGES ABI
@@ -16693,7 +16693,7 @@
 	echo "* (otherwise, a default of CFLAGS=-O3 will be used)    *"
 	echo "********************************************************"
 	echo ""
-        CFLAGS="-O3"
+        CFLAGS="-O2"
   fi
 
   as_CACHEVAR=`$as_echo "ax_cv_check_cflags__$CFLAGS" | $as_tr_sh`
Index: thunderbird-52.0/mozilla/js/src/ctypes/libffi/m4/ax_cc_maxopt.m4
===================================================================
--- thunderbird-52.0/mozilla/js/src/ctypes/libffi/m4/ax_cc_maxopt.m4
+++ thunderbird-52.0/mozilla/js/src/ctypes/libffi/m4/ax_cc_maxopt.m4	2017-04-12 12:26:13.892407658 -0400
@@ -138,7 +138,7 @@
 
     gnu)
      # default optimization flags for gcc on all systems
-     CFLAGS="-O3 -fomit-frame-pointer"
+     CFLAGS="-O2 -fomit-frame-pointer"
 
      # -malign-double for x86 systems
      # LIBFFI -- DON'T DO THIS - CHANGES ABI
@@ -163,7 +163,7 @@
 	echo "* (otherwise, a default of CFLAGS=-O3 will be used)    *"
 	echo "********************************************************"
 	echo ""
-        CFLAGS="-O3"
+        CFLAGS="-O2"
   fi
 
   AX_CHECK_COMPILE_FLAG($CFLAGS, [], [
Index: thunderbird-52.0/mozilla/modules/freetype2/builds/compiler/gcc.mk
===================================================================
--- thunderbird-52.0/mozilla/modules/freetype2/builds/compiler/gcc.mk
+++ thunderbird-52.0/mozilla/modules/freetype2/builds/compiler/gcc.mk	2017-04-12 12:30:59.162841529 -0400
@@ -61,7 +61,7 @@
 #   Use the ANSIFLAGS variable to define the compiler flags used to enfore
 #   ANSI compliance.
 #
-CFLAGS ?= -c -g -O3 -Wall
+CFLAGS ?= -c -g -O2 -Wall
 
 # ANSIFLAGS: Put there the flags used to make your compiler ANSI-compliant.
 #
Index: thunderbird-52.0/mozilla/security/nss/coreconf/mkdepend/Makefile
===================================================================
--- thunderbird-52.0/mozilla/security/nss/coreconf/mkdepend/Makefile
+++ thunderbird-52.0/mozilla/security/nss/coreconf/mkdepend/Makefile	2017-04-12 12:31:38.682901632 -0400
@@ -41,7 +41,7 @@
 include $(DEPTH)/coreconf/rules.mk
 
 ifdef GNU_CC
-OPTIMIZER = -O3
+OPTIMIZER = -O2
 else
 ifeq ($(OS_ARCH),SunOS)
 OPTIMIZER = -fast
Index: thunderbird-52.0/mozilla/browser/components/translation/cld2/Makefile
===================================================================
--- thunderbird-52.0/mozilla/browser/components/translation/cld2/Makefile
+++ thunderbird-52.0/mozilla/browser/components/translation/cld2/Makefile	2017-04-12 12:16:07.799489652 -0400
@@ -19,7 +19,7 @@
 # Unfortunately, once the heap has been enlarged, there is no shrinking, so
 # analyzing one 20MB web page gives us a 30-40MB heap for the life of the
 # worker.
-FLAGS=-s -O3 -s INLINING_LIMIT=1 -s NO_FILESYSTEM=1 -s NO_EXIT_RUNTIME=1 -s INVOKE_RUN=0 \
+FLAGS=-s -O2 -s INLINING_LIMIT=1 -s NO_FILESYSTEM=1 -s NO_EXIT_RUNTIME=1 -s INVOKE_RUN=0 \
       -s TOTAL_STACK=8192 -s TOTAL_MEMORY=2097152 -s ALLOW_MEMORY_GROWTH=1 \
       --llvm-lto 1 --memory-init-file 1 --closure 1