diff -up thunderbird-45.4.0/mozilla/configure.in.pgo thunderbird-45.4.0/mozilla/configure.in
--- thunderbird-45.4.0/mozilla/configure.in.pgo	2016-10-01 22:57:35.758907539 +0200
+++ thunderbird-45.4.0/mozilla/configure.in	2016-10-01 23:39:20.858686486 +0200
@@ -2114,7 +2114,7 @@ ia64*-hpux*)
         # while; Intel recommends against using it.
         MOZ_OPTIMIZE_FLAGS="-O2"
     elif test "$GNU_CC" -o "$GNU_CXX"; then
-        MOZ_PGO_OPTIMIZE_FLAGS="-O3"
+        MOZ_PGO_OPTIMIZE_FLAGS="-O2"
         MOZ_OPTIMIZE_FLAGS=""
         if test -z "$CLANG_CC"; then
            MOZ_OPTIMIZE_FLAGS="-freorder-blocks $MOZ_OPTIMIZE_FLAGS"
diff -up thunderbird-45.4.0/mozilla/js/src/configure.in.pgo thunderbird-45.4.0/mozilla/js/src/configure.in
--- thunderbird-45.4.0/mozilla/js/src/configure.in.pgo	2016-10-01 22:57:35.758907539 +0200
+++ thunderbird-45.4.0/mozilla/js/src/configure.in	2016-10-01 23:44:08.571989111 +0200
@@ -1650,7 +1650,7 @@ ia64*-hpux*)
         # while; Intel recommends against using it.
         MOZ_OPTIMIZE_FLAGS="-O2"
     elif test "$GNU_CC" -o "$GNU_CXX"; then
-        MOZ_PGO_OPTIMIZE_FLAGS="-O3"
+        MOZ_PGO_OPTIMIZE_FLAGS="-O2"
         MOZ_OPTIMIZE_FLAGS="-O2"
         if test -z "$CLANG_CC"; then
            MOZ_OPTIMIZE_FLAGS="-freorder-blocks $MOZ_OPTIMIZE_FLAGS"