--- a/moz.configure
+++ b/moz.configure
@@ -526,16 +526,18 @@ def nsis_binary_type(nsis):
 @depends(host)
 def nsis_flags(host):
     if host.kernel != 'WINNT':
         return '-nocd'
     return ''
 
 set_config('MAKENSISU_FLAGS', nsis_flags)
 
+check_prog('7Z', ('7z', '7za'), allow_missing=True, when=target_is_windows)
+
 # Fallthrough to autoconf-based configure
 include('build/moz.configure/old.configure')
 
 @imports('__sandbox__')
 def all_paths():
     return __sandbox__._all_paths
 
 set_config('ALL_CONFIGURE_PATHS', all_paths())

--- a/toolkit/mozapps/installer/windows/nsis/makensis.mk
+++ b/toolkit/mozapps/installer/windows/nsis/makensis.mk
@@ -47,17 +47,17 @@ CUSTOM_UI = \
 	$(INSTALL) $(addprefix $(MOZILLA_DIR)/other-licenses/nsis/,$(CUSTOM_UI)) $(CONFIG_DIR)
 	cd $(CONFIG_DIR) && $(MAKENSISU) $(MAKENSISU_FLAGS) installer.nsi
 ifdef MOZ_STUB_INSTALLER
 	cd $(CONFIG_DIR) && $(MAKENSISU) $(MAKENSISU_FLAGS) stub.nsi
 ifdef MOZ_EXTERNAL_SIGNING_FORMAT
 	$(MOZ_SIGN_CMD) $(foreach f,$(MOZ_EXTERNAL_SIGNING_FORMAT),-f $(f)) $(CONFIG_DIR)/setup-stub.exe
 endif
 	$(MAKE) $(CONFIG_DIR)/7zSD.sfx
-	cd $(CONFIG_DIR) &&  $(CYGWIN_WRAPPER) 7z a -t7z $(ABS_CONFIG_DIR)/stub.7z setup-stub.exe -mx -m0=BCJ2 -m1=LZMA:d21 -m2=LZMA:d17 -m3=LZMA:d17 -mb0:1 -mb0s1:2 -mb0s2:3
+	cd $(CONFIG_DIR) &&  $(CYGWIN_WRAPPER) $(7Z) a -t7z $(ABS_CONFIG_DIR)/stub.7z setup-stub.exe -mx -m0=BCJ2 -m1=LZMA:d21 -m2=LZMA:d17 -m3=LZMA:d17 -mb0:1 -mb0s1:2 -mb0s2:3
 	cat $(CONFIG_DIR)/7zSD.sfx $(CONFIG_DIR)/stub.tag $(CONFIG_DIR)/stub.7z > "$(CONFIG_DIR)/stub.exe"
 ifdef MOZ_EXTERNAL_SIGNING_FORMAT_STUB
 	$(MOZ_SIGN_CMD) $(foreach f,$(MOZ_EXTERNAL_SIGNING_FORMAT_STUB),-f $(f)) $(CONFIG_DIR)/stub.exe
 endif
 endif
 # Support for building the uninstaller when repackaging locales
 ifeq ($(CONFIG_DIR),l10ngen)
 	cd $(CONFIG_DIR) && $(MAKENSISU) $(MAKENSISU_FLAGS) uninstaller.nsi
@@ -66,17 +66,17 @@ ifdef MOZ_EXTERNAL_SIGNING_FORMAT
 	$(MOZ_SIGN_CMD) $(foreach f,$(MOZ_EXTERNAL_SIGNING_FORMAT),-f $(f)) "$@"
 endif
 
 $(CONFIG_DIR)/7zSD.sfx:
 	$(CYGWIN_WRAPPER) upx --best -o $(CONFIG_DIR)/7zSD.sfx $(SFX_MODULE)
 
 installer::
 	$(INSTALL) $(CONFIG_DIR)/setup.exe $(DEPTH)/installer-stage
-	cd $(DEPTH)/installer-stage && $(CYGWIN_WRAPPER) 7z a -r -t7z $(ABS_CONFIG_DIR)/app.7z -mx -m0=BCJ2 -m1=LZMA:d25 -m2=LZMA:d19 -m3=LZMA:d19 -mb0:1 -mb0s1:2 -mb0s2:3
+	cd $(DEPTH)/installer-stage && $(CYGWIN_WRAPPER) $(7Z) a -r -t7z $(ABS_CONFIG_DIR)/app.7z -mx -m0=BCJ2 -m1=LZMA:d25 -m2=LZMA:d19 -m3=LZMA:d19 -mb0:1 -mb0s1:2 -mb0s2:3
 	$(MAKE) $(CONFIG_DIR)/7zSD.sfx
 	$(NSINSTALL) -D $(DIST)/$(PKG_INST_PATH)
 	cat $(CONFIG_DIR)/7zSD.sfx $(CONFIG_DIR)/app.tag $(CONFIG_DIR)/app.7z > "$(DIST)/$(PKG_INST_PATH)$(PKG_INST_BASENAME).exe"
 	chmod 0755 "$(DIST)/$(PKG_INST_PATH)$(PKG_INST_BASENAME).exe"
 ifdef MOZ_STUB_INSTALLER
 	cp $(CONFIG_DIR)/stub.exe "$(DIST)/$(PKG_INST_PATH)$(PKG_STUB_BASENAME).exe"
 	chmod 0755 "$(DIST)/$(PKG_INST_PATH)$(PKG_STUB_BASENAME).exe"
 endif