diff --git a/config/Makefile.in b/config/Makefile.in
index e73d3a0ce3a..62683ac0aa8 100644
--- a/config/Makefile.in
+++ b/config/Makefile.in
@@ -10,10 +10,6 @@ ifdef NSBUILDROOT
 override NSBUILDROOT :=
 endif
 
-ifdef GNU_CC
-MODULE_OPTIMIZE_FLAGS = -O3
-endif
-
 include $(topsrcdir)/config/config.mk
 
 # L10n jobs are doing make -C config manually before anything else,
diff --git a/config/moz.build b/config/moz.build
index dbf819cb989..180e070de38 100644
--- a/config/moz.build
+++ b/config/moz.build
@@ -39,3 +39,6 @@ PYTHON_UNIT_TESTS += [
     'tests/unit-nsinstall.py',
     'tests/unit-printprereleasesuffix.py',
 ]
+
+if CONFIG['GNU_CC'] and CONFIG['MOZ_OPTIMIZE']:
+    CFLAGS += ['-O3']
diff --git a/gfx/cairo/cairo/src/Makefile.in b/gfx/cairo/cairo/src/Makefile.in
index f707f65534d..3f9653ee3dc 100644
--- a/gfx/cairo/cairo/src/Makefile.in
+++ b/gfx/cairo/cairo/src/Makefile.in
@@ -2,12 +2,6 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-ifdef GNU_CC
-ifeq ($(OS_TARGET),Android)
-MODULE_OPTIMIZE_FLAGS = -O2
-endif
-endif
-
 INSTALL_TARGETS += cairo_features
 cairo_features_FILES := cairo-features.h
 cairo_features_DEST = $(DIST)/include/cairo
diff --git a/gfx/cairo/cairo/src/moz.build b/gfx/cairo/cairo/src/moz.build
index e99fcc97a95..88babf740a5 100644
--- a/gfx/cairo/cairo/src/moz.build
+++ b/gfx/cairo/cairo/src/moz.build
@@ -234,6 +234,11 @@ if CONFIG['GNU_CC']:
             '-Wno-error=uninitialized',
         ]
 
+# See bug 386897.
+if CONFIG['GNU_CC'] and CONFIG['OS_TARGET'] == 'Android' and CONFIG['MOZ_OPTIMIZE']:
+    CFLAGS += ['-O2']
+    CXXFLAGS += ['-O2']
+
 if CONFIG['MOZ_WIDGET_TOOLKIT'] == 'qt':
     CFLAGS += CONFIG['MOZ_QT_CFLAGS']
     CXXFLAGS += CONFIG['MOZ_QT_CFLAGS']
diff --git a/gfx/cairo/libpixman/src/Makefile.in b/gfx/cairo/libpixman/src/Makefile.in
index 041c7bf73ab..f119333b446 100644
--- a/gfx/cairo/libpixman/src/Makefile.in
+++ b/gfx/cairo/libpixman/src/Makefile.in
@@ -2,10 +2,6 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-ifeq ($(OS_TARGET),Android)
-MODULE_OPTIMIZE_FLAGS = -O2
-endif
-
 include $(topsrcdir)/config/rules.mk
 
 # The ARM asm functions here don't appreciate being called by functions
diff --git a/gfx/cairo/libpixman/src/moz.build b/gfx/cairo/libpixman/src/moz.build
index f1bfd83642d..2eb6ef62e57 100644
--- a/gfx/cairo/libpixman/src/moz.build
+++ b/gfx/cairo/libpixman/src/moz.build
@@ -145,3 +145,7 @@ if CONFIG['GNU_CC']:
             '-Wno-tautological-compare',
             '-Wno-tautological-constant-out-of-range-compare',
         ]
+
+# See bug 386897.
+if CONFIG['OS_TARGET'] == 'Android' and CONFIG['MOZ_OPTIMIZE']:
+    CFLAGS += ['-O2']
diff --git a/memory/mozjemalloc/Makefile.in b/memory/mozjemalloc/Makefile.in
index ac7ff1eeb61..88aeccf6fc6 100644
--- a/memory/mozjemalloc/Makefile.in
+++ b/memory/mozjemalloc/Makefile.in
@@ -9,11 +9,5 @@ ifndef MOZ_JEMALLOC3
 # broken when compiling without optimization, while avoiding to add yet another
 # configure test.
 MOZ_OPTIMIZE = 1
-
-ifeq ($(OS_ARCH),SunOS)
-ifndef GNU_CC
-MODULE_OPTIMIZE_FLAGS = -xO5
-endif
-endif
 endif
 
diff --git a/memory/mozjemalloc/moz.build b/memory/mozjemalloc/moz.build
index b912bc95f1b..2b223f4817a 100644
--- a/memory/mozjemalloc/moz.build
+++ b/memory/mozjemalloc/moz.build
@@ -16,6 +16,11 @@ if not CONFIG['MOZ_JEMALLOC3']:
     STATIC_LIBRARY_NAME = 'jemalloc'
     FORCE_STATIC_LIB = True
 
+    # See bug 422055.
+    if CONFIG['OS_ARCH'] == 'SunOS' and not CONFIG['GNU_CC'] \
+            and CONFIG['MOZ_OPTIMIZE']:
+        CFLAGS += ['-xO5']
+
 # For non release/esr builds, enable (some) fatal jemalloc assertions.  This
 # helps us catch memory errors.
 if CONFIG['MOZ_UPDATE_CHANNEL'] not in ('release', 'esr'):