--- Waterfox-56.2.4/config/Makefile.in
+++ Waterfox-56.2.4/config/Makefile.in
@@ -41,6 +41,7 @@
 	$(PYTHON) -m mozbuild.action.preprocessor $(DEFINES) $(ACDEFINES) \
 		-DMOZ_TREE_CAIRO=$(MOZ_TREE_CAIRO) \
 		-DMOZ_TREE_PIXMAN=$(MOZ_TREE_PIXMAN) \
+		-DMOZ_SYSTEM_HARFBUZZ=$(MOZ_SYSTEM_HARFBUZZ) \
 		-DMOZ_SYSTEM_HUNSPELL=$(MOZ_SYSTEM_HUNSPELL) \
 		-DMOZ_SYSTEM_BZ2=$(MOZ_SYSTEM_BZ2) \
 		-DMOZ_SYSTEM_ZLIB=$(MOZ_SYSTEM_ZLIB) \
--- Waterfox-56.2.4/config/system-headers
+++ Waterfox-56.2.4/config/system-headers
@@ -1274,6 +1274,11 @@
 libsn/sn-monitor.h
 libsn/sn-util.h
 #endif
+#if MOZ_SYSTEM_HARFBUZZ==1
+harfbuzz/hb-glib.h
+harfbuzz/hb-ot.h
+harfbuzz/hb.h
+#endif
 #if MOZ_SYSTEM_HUNSPELL==1
 hunspell.hxx
 #endif
--- Waterfox-56.2.4/dom/base/moz.build
+++ Waterfox-56.2.4/dom/base/moz.build
@@ -476,6 +476,9 @@
 if CONFIG['MOZ_X11']:
     CXXFLAGS += CONFIG['TK_CFLAGS']
 
+if CONFIG['MOZ_SYSTEM_HARFBUZZ']:
+    CXXFLAGS += CONFIG['MOZ_HARFBUZZ_CFLAGS']
+
 GENERATED_FILES += [
     'PropertyUseCounterMap.inc',
     'UseCounterList.h',
--- Waterfox-56.2.4/gfx/harfbuzz/README-mozilla
+++ Waterfox-56.2.4/gfx/harfbuzz/README-mozilla
@@ -19,3 +19,8 @@
 
 If the collection of source files changes, manual updates to moz.build may be
 needed, as we don't use the upstream makefiles.
+
+The in-tree copy may be omitted during build by --with-system-harfbuzz.
+Make sure to keep pkg-config version check within toolkit/moz.configure in sync
+with checkout version or increment latest tag by one if it's not based
+on upstream release.
--- Waterfox-56.2.4/gfx/moz.build
+++ Waterfox-56.2.4/gfx/moz.build
@@ -10,6 +10,9 @@
 if CONFIG['MOZ_TREE_CAIRO']:
     DIRS += ['cairo']
 
+if not CONFIG['MOZ_SYSTEM_HARFBUZZ']:
+    DIRS += ['harfbuzz/src']
+
 DIRS += [
     '2d',
     'ycbcr',
@@ -19,7 +22,6 @@
     'gl',
     'layers',
     'graphite2/src',
-    'harfbuzz/src',
     'ots/src',
     'thebes',
     'ipc',
--- Waterfox-56.2.4/gfx/skia/generate_mozbuild.py
+++ Waterfox-56.2.4/gfx/skia/generate_mozbuild.py
@@ -148,6 +148,9 @@
         '-Wno-unused-private-field',
     ]
 
+if CONFIG['MOZ_SYSTEM_HARFBUZZ']:
+    CXXFLAGS += CONFIG['MOZ_HARFBUZZ_CFLAGS']
+
 if CONFIG['MOZ_WIDGET_TOOLKIT'] in ('gtk3', 'android'):
     CXXFLAGS += CONFIG['MOZ_CAIRO_CFLAGS']
     CXXFLAGS += CONFIG['CAIRO_FT_CFLAGS']
--- Waterfox-56.2.4/gfx/skia/moz.build
+++ Waterfox-56.2.4/gfx/skia/moz.build
@@ -823,6 +823,9 @@
         '-Wno-unused-private-field',
     ]
 
+if CONFIG['MOZ_SYSTEM_HARFBUZZ']:
+    CXXFLAGS += CONFIG['MOZ_HARFBUZZ_CFLAGS']
+
 if CONFIG['MOZ_WIDGET_TOOLKIT'] in ('gtk3', 'android'):
     CXXFLAGS += CONFIG['MOZ_CAIRO_CFLAGS']
     CXXFLAGS += CONFIG['CAIRO_FT_CFLAGS']
--- Waterfox-56.2.4/gfx/thebes/moz.build
+++ Waterfox-56.2.4/gfx/thebes/moz.build
@@ -273,6 +273,9 @@
 
 DEFINES['GRAPHITE2_STATIC'] = True
 
+if CONFIG['MOZ_SYSTEM_HARFBUZZ']:
+    CXXFLAGS += CONFIG['MOZ_HARFBUZZ_CFLAGS']
+
 if CONFIG['CLANG_CXX']:
     # Suppress warnings from Skia header files.
     SOURCES['gfxPlatform.cpp'].flags += ['-Wno-implicit-fallthrough']
--- Waterfox-56.2.4/intl/unicharutil/util/moz.build
+++ Waterfox-56.2.4/intl/unicharutil/util/moz.build
@@ -29,4 +29,7 @@
         'ICUUtils.cpp',
     ]
 
+if CONFIG['MOZ_SYSTEM_HARFBUZZ']:
+    CXXFLAGS += CONFIG['MOZ_HARFBUZZ_CFLAGS']
+
 FINAL_LIBRARY = 'xul'
--- Waterfox-56.2.4/netwerk/dns/moz.build
+++ Waterfox-56.2.4/netwerk/dns/moz.build
@@ -69,6 +69,9 @@
     '/netwerk/base',
 ]
 
+if CONFIG['MOZ_SYSTEM_HARFBUZZ']:
+    CXXFLAGS += CONFIG['MOZ_HARFBUZZ_CFLAGS']
+
 if CONFIG['ENABLE_INTL_API']:
     DEFINES['IDNA2008'] = True
     USE_LIBS += ['icu']
--- Waterfox-56.2.4/toolkit/library/moz.build
+++ Waterfox-56.2.4/toolkit/library/moz.build
@@ -212,6 +212,9 @@
 if CONFIG['MOZ_SYSTEM_PNG']:
     OS_LIBS += CONFIG['MOZ_PNG_LIBS']
 
+if CONFIG['MOZ_SYSTEM_HARFBUZZ']:
+    OS_LIBS += CONFIG['MOZ_HARFBUZZ_LIBS']
+
 if CONFIG['MOZ_SYSTEM_WEBP']:
     OS_LIBS += CONFIG['MOZ_WEBP_LIBS']
 
--- Waterfox-56.2.4/toolkit/moz.configure
+++ Waterfox-56.2.4/toolkit/moz.configure
@@ -314,6 +314,16 @@
 add_old_configure_assignment('_HAVE_FREETYPE2',
                              depends_if(freetype2_info)(lambda _: True))
 
+# HarfBuzz
+# ==============================================================
+option('--with-system-harfbuzz',
+       help="Use system harfbuzz (located with pkgconfig)")
+
+system_harfbuzz = pkg_check_modules('MOZ_HARFBUZZ', 'harfbuzz >= 1.4.2',
+                                    when='--with-system-harfbuzz')
+
+set_config('MOZ_SYSTEM_HARFBUZZ', depends_if(system_harfbuzz)(lambda _: True))
+
 # Apple platform decoder support
 # ==============================================================
 @depends(toolkit)