--- a/Makefile.in
+++ b/Makefile.in
@@ -42,20 +42,27 @@ VPATH		= @srcdir@
 include $(DEPTH)/config/autoconf.mk
 
 default::
 
 include $(topsrcdir)/$(MOZ_BUILD_APP)/build.mk
 
 include $(topsrcdir)/config/config.mk
 
-default export libs clean realclean distclean alldep maybe_clobber_profiledbuild rebase uploadsymbols signnss deliver \
-check mochitest mochitest-plain mochitest-chrome mochitest-browser-chrome mochitest-a11y reftest crashtest xpcshell-tests::
+default export libs clean realclean distclean alldep maybe_clobber_profiledbuild rebase uploadsymbols signnss deliver::
 	$(MAKE) -C mozilla $@
 
+ifdef ENABLE_TESTS
+check \
+mochitest mochitest-plain mochitest-chrome mochitest-browser-chrome mochitest-a11y \
+reftest crashtest \
+xpcshell-tests::
+	$(MAKE) -C mozilla $@
+endif
+
 # http://bugzilla.mozilla.org/show_bug.cgi?id=450485
 MAKE_SYM_STORE_PATH=dist/bin
 ifeq ($(OS_ARCH),Darwin)
 ifdef UNIVERSAL_BINARY
   MAKE_SYM_STORE_PATH=dist/universal
 endif
 endif
 ifeq ($(OS_ARCH),WINNT)

--- a/config/rules.mk
+++ b/config/rules.mk
@@ -146,36 +146,37 @@ libs::
 	$(foreach dir,$(XPCSHELL_TESTS),$(_INSTALL_TESTS))
 	$(PERL) -I$(MOZILLA_DIR)/config $(MOZILLA_DIR)/config/build-list.pl \
 	  $(testxpcobjdir)/all-test-dirs.list \
 	  $(addprefix $(MODULE)/,$(XPCSHELL_TESTS))
 
 testxpcsrcdir = $(MOZILLA_SRCDIR)/testing/xpcshell
 
 # Execute all tests in the $(XPCSHELL_TESTS) directories.
-check::
-	$(PYTHON) \
+# See also mozilla/testsuite-targets.mk 'xpcshell-tests' target for global execution.
+xpcshell-tests:
+	$(PYTHON) -u \
           $(testxpcsrcdir)/runxpcshelltests.py \
           $(DIST)/bin/xpcshell \
           $(foreach dir,$(XPCSHELL_TESTS),$(testxpcobjdir)/$(MODULE)/$(dir))
 
 # Execute a single test, specified in $(SOLO_FILE), but don't automatically
 # start the test. Instead, present the xpcshell prompt so the user can
 # attach a debugger and then start the test.
-check-interactive::
-	$(PYTHON) \
+check-interactive:
+	$(PYTHON) -u \
           $(testxpcsrcdir)/runxpcshelltests.py \
           --test=$(SOLO_FILE) \
           --interactive \
           $(DIST)/bin/xpcshell \
           $(foreach dir,$(XPCSHELL_TESTS),$(testxpcobjdir)/$(MODULE)/$(dir))
 
 # Execute a single test, specified in $(SOLO_FILE)
-check-one::
-	$(PYTHON) \
+check-one:
+	$(PYTHON) -u \
           $(testxpcsrcdir)/runxpcshelltests.py \
           --test=$(SOLO_FILE) \
           $(DIST)/bin/xpcshell \
           $(foreach dir,$(XPCSHELL_TESTS),$(testxpcobjdir)/$(MODULE)/$(dir))
 
 endif # XPCSHELL_TESTS
 
 ifdef CPP_UNIT_TESTS
@@ -192,16 +193,18 @@ LIBS += $(XPCOM_GLUE_LDOPTS) $(NSPR_LIBS
 check::
 	@$(EXIT_ON_ERROR) \
 	  for f in $(subst .cpp,,$(CPP_UNIT_TESTS)); do \
 	    XPCOM_DEBUG_BREAK=stack-and-abort $(RUN_TEST_PROGRAM) $(DIST)/bin/$$f; \
 	  done
 
 endif # CPP_UNIT_TESTS
 
+.PHONY: check xpcshell-tests check-interactive check-one
+
 endif # ENABLE_TESTS
 
 
 #
 # Library rules
 #
 # If BUILD_STATIC_LIBS or FORCE_STATIC_LIB is set, build a static library.
 # Otherwise, build a shared library.
@@ -2026,17 +2029,17 @@ endif
 # hundreds of built-in suffix rules for stuff we don't need.
 #
 .SUFFIXES:
 
 #
 # Fake targets.  Always run these rules, even if a file/directory with that
 # name already exists.
 #
-.PHONY: all all_platforms alltags boot checkout chrome realchrome clean clobber clobber_all export install libs makefiles realclean run_viewer run_apprunner tools $(DIRS) $(TOOL_DIRS) FORCE check check-interactive check-one
+.PHONY: all all_platforms alltags boot checkout chrome realchrome clean clobber clobber_all export install libs makefiles realclean run_viewer run_apprunner tools $(DIRS) $(TOOL_DIRS) FORCE
 
 # Used as a dependency to force targets to rebuild
 FORCE:
 
 # Delete target if error occurs when building target
 .DELETE_ON_ERROR:
 
 # Properly set LIBPATTERNS for the platform
@@ -2164,12 +2167,14 @@ ifneq (,$(filter $(PROGRAM) $(SIMPLE_PRO
 endif
 	+$(LOOP_OVER_PARALLEL_DIRS)
 	+$(LOOP_OVER_DIRS)
 
 documentation:
 	@cd $(DEPTH)
 	$(DOXYGEN) $(DEPTH)/config/doxygen.cfg
 
+ifdef ENABLE_TESTS
 check:: $(SUBMAKEFILES) $(MAKE_DIRS)
 	+$(LOOP_OVER_PARALLEL_DIRS)
 	+$(LOOP_OVER_DIRS)
 	+$(LOOP_OVER_TOOL_DIRS)
+endif