diff --git a/build/automation-build.mk b/build/automation-build.mk
deleted file mode 100644
index e25f90c5d3ab..000000000000
--- a/build/automation-build.mk
+++ /dev/null
@@ -1,67 +0,0 @@
-# This Source Code Form is subject to the terms of the Mozilla Public
-# 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/.
-
-include $(MOZILLA_DIR)/build/binary-location.mk
-
-browser_path := '"$(browser_path)"'
-
-_PROFILE_DIR = $(TARGET_DEPTH)/_profile/pgo
-
-ABSOLUTE_TOPSRCDIR = $(abspath $(MOZILLA_DIR))
-_CERTS_SRC_DIR = $(ABSOLUTE_TOPSRCDIR)/build/pgo/certs
-
-AUTOMATION_PPARGS = 	\
-			-DBROWSER_PATH=$(browser_path) \
-			-DXPC_BIN_PATH='"$(DIST)/bin"' \
-			-DBIN_SUFFIX='"$(BIN_SUFFIX)"' \
-			-DPROFILE_DIR='"$(_PROFILE_DIR)"' \
-			-DCERTS_SRC_DIR='"$(_CERTS_SRC_DIR)"' \
-			-DPERL='"$(PERL)"' \
-			$(NULL)
-
-ifeq ($(OS_ARCH),Darwin)
-AUTOMATION_PPARGS += -DIS_MAC=1
-else
-AUTOMATION_PPARGS += -DIS_MAC=0
-endif
-
-ifeq ($(OS_ARCH),Linux)
-AUTOMATION_PPARGS += -DIS_LINUX=1
-else
-AUTOMATION_PPARGS += -DIS_LINUX=0
-endif
-
-ifeq ($(host_os), cygwin)
-AUTOMATION_PPARGS += -DIS_CYGWIN=1
-endif
-
-ifeq ($(ENABLE_TESTS), 1)
-AUTOMATION_PPARGS += -DIS_TEST_BUILD=1
-else
-AUTOMATION_PPARGS += -DIS_TEST_BUILD=0
-endif
-
-ifeq ($(MOZ_DEBUG), 1)
-AUTOMATION_PPARGS += -DIS_DEBUG_BUILD=1
-else
-AUTOMATION_PPARGS += -DIS_DEBUG_BUILD=0
-endif
-
-ifdef MOZ_CRASHREPORTER
-AUTOMATION_PPARGS += -DCRASHREPORTER=1
-else
-AUTOMATION_PPARGS += -DCRASHREPORTER=0
-endif
-
-ifdef MOZ_ASAN
-AUTOMATION_PPARGS += -DIS_ASAN=1
-else
-AUTOMATION_PPARGS += -DIS_ASAN=0
-endif
-
-automation.py: $(MOZILLA_DIR)/build/automation.py.in $(MOZILLA_DIR)/build/automation-build.mk
-	$(call py_action,preprocessor, \
-	$(AUTOMATION_PPARGS) $(DEFINES) $(ACDEFINES) $< -o $@)
-
-GARBAGE += automation.py automation.pyc
diff --git a/build/automation.py.in b/build/automation.py.in
index 60c252c072d3..99c633b0de3d 100644
--- a/build/automation.py.in
+++ b/build/automation.py.in
@@ -53,7 +53,6 @@ _IS_CYGWIN = False
 #endif
 #expand _BIN_SUFFIX = __BIN_SUFFIX__
 
-#expand _DEFAULT_APP = "./" + __BROWSER_PATH__
 #expand _CERTS_SRC_DIR = __CERTS_SRC_DIR__
 #expand _IS_TEST_BUILD = __IS_TEST_BUILD__
 #expand _IS_DEBUG_BUILD = __IS_DEBUG_BUILD__
@@ -99,7 +98,6 @@ class Automation(object):
 
   UNIXISH = not IS_WIN32 and not IS_MAC
 
-  DEFAULT_APP = _DEFAULT_APP
   CERTS_SRC_DIR = _CERTS_SRC_DIR
   IS_TEST_BUILD = _IS_TEST_BUILD
   IS_DEBUG_BUILD = _IS_DEBUG_BUILD
@@ -138,7 +136,6 @@ class Automation(object):
            "runApp",
            "Process",
            "DIST_BIN",
-           "DEFAULT_APP",
            "CERTS_SRC_DIR",
            "environment",
            "IS_TEST_BUILD",
diff --git a/build/gen_automation.py b/build/gen_automation.py
new file mode 100644
index 000000000000..24b89862e6ef
--- /dev/null
+++ b/build/gen_automation.py
@@ -0,0 +1,48 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distibuted with this
+# file, You can obtain one at http://mozilla.og/MPL/2.0/.
+
+import sys
+import buildconfig
+from mozbuild.preprocessor import Preprocessor
+
+
+def main(output, input_file):
+    pp = Preprocessor()
+    pp.context.update(buildconfig.defines['ALLDEFINES'])
+
+    substs = buildconfig.substs
+
+    # Substs taken verbatim.
+    substs_vars = (
+        'BIN_SUFFIX',
+    )
+    for var in substs_vars:
+        pp.context[var] = '"%s"' % substs[var]
+
+    # Derived values.
+    for key, condition in (
+            ('IS_MAC', substs['OS_ARCH'] == 'Darwin'),
+            ('IS_LINUX', substs['OS_ARCH'] == 'Linux'),
+            ('IS_TEST_BUILD', substs.get('ENABLE_TESTS') == '1'),
+            ('IS_DEBUG_BUILD', substs.get('MOZ_DEBUG') == '1'),
+            ('CRASHREPORTER', substs.get('MOZ_CRASHREPORTER')),
+            ('IS_ASAN', substs.get('MOZ_ASAN'))):
+        if condition:
+            pp.context[key] = '1'
+        else:
+            pp.context[key] = '0'
+
+    pp.context.update({
+        'XPC_BIN_PATH': '"%s/dist/bin"' % buildconfig.topobjdir,
+        'CERTS_SRC_DIR': '"%s/build/pgo/certs"' % buildconfig.topsrcdir,
+    })
+
+    pp.out = output
+    pp.do_include(input_file)
+
+
+if __name__ == '__main__':
+    main(*sys.agv[1:])
diff --git a/build/moz.build b/build/moz.build
index 2f2d3efd64f3..64b4f8e5f5eb 100644
--- a/build/moz.build
+++ b/build/moz.build
@@ -96,6 +96,20 @@ if CONFIG['MOZ_APP_BASENAME']:
     appini.script = 'appini_header.py'
     appini.inputs = ['!application.ini']
 
+if CONFIG['ENABLE_TESTS']:
+    GENERATED_FILES += ['automation.py']
+    auto = GENERATED_FILES['automation.py']
+    auto.script = 'gen_automation.py'
+    auto.inputs = ['automation.py.in']
+
+    TEST_HARNESS_FILES.reftest += [
+        '!automation.py',
+    ]
+
+    TEST_HARNESS_FILES.testing.mochitest += [
+        '!automation.py',
+    ]
+
 # NOTE: Keep .gdbinit in the topsrcdir for people who run gdb from the topsrcdir.
 OBJDIR_FILES += ['/.gdbinit']
 
diff --git a/layout/tools/reftest/Makefile.in b/layout/tools/reftest/Makefile.in
index 7ff59cd8b6af..1baf9594bc2b 100644
--- a/layout/tools/reftest/Makefile.in
+++ b/layout/tools/reftest/Makefile.in
@@ -7,10 +7,6 @@ _DEST_DIR = $(DEPTH)/_tests/reftest
 
 include $(topsrcdir)/config/rules.mk
 
-# We're installing to _tests/reftest
-TARGET_DEPTH = ../..
-include $(topsrcdir)/build/automation-build.mk
-
 # copy harness and the reftest extension bits to $(_DEST_DIR)
 # This needs to happen after jar.mn handling from rules.mk included above.
 # The order of the :: rules ensures that.
diff --git a/layout/tools/reftest/moz.build b/layout/tools/reftest/moz.build
index b307d9affb90..ad6bea5cef53 100644
--- a/layout/tools/reftest/moz.build
+++ b/layout/tools/reftest/moz.build
@@ -14,9 +14,7 @@ JAR_MANIFESTS += ['jar.mn']
 FINAL_TARGET_PP_FILES += ['install.rdf']
 FINAL_TARGET_FILES += ['bootstrap.js']
 
-GENERATED_FILES += ['automation.py']
 TEST_HARNESS_FILES.reftest += [
-    '!automation.py',
     '/build/mobile/remoteautomation.py',
     '/build/pgo/server-locations.txt',
     '/testing/mochitest/server.js',
diff --git a/python/mozbuild/mozbuild/backend/tup.py b/python/mozbuild/mozbuild/backend/tup.py
index acb0982c6d0b..94d50e9dd1dd 100644
--- a/python/mozbuild/mozbuild/backend/tup.py
+++ b/python/mozbuild/mozbuild/backend/tup.py
@@ -569,7 +569,8 @@ class TupBackend(CommonBackend):
                 if exports:
                     backend_file.export(exports)
 
-            if any(f in obj.outputs for f in ('source-repo.h', 'buildid.h')):
+            if any(f.endswith(('automation.py', 'source-repo.h', 'buildid.h'))
+                   for f in obj.outputs):
                 extra_outputs = [self._early_generated_files]
             else:
                 extra_outputs = [self._installed_files] if obj.required_for_compile else []
diff --git a/testing/mochitest/Makefile.in b/testing/mochitest/Makefile.in
index 861c273dc7a1..91b422c4815f 100644
--- a/testing/mochitest/Makefile.in
+++ b/testing/mochitest/Makefile.in
@@ -7,10 +7,6 @@
 _DEST_DIR = $(DEPTH)/_tests/$(relativesrcdir)
 
 include $(topsrcdir)/config/rules.mk
-# We're installing to _tests/testing/mochitest, so this is the depth
-# necessary for relative objdir paths.
-TARGET_DEPTH = ../../..
-include $(topsrcdir)/build/automation-build.mk
 
 libs:: 
 	(cd $(DIST)/xpi-stage && tar $(TAR_CREATE_FLAGS) - mochijar) | (cd $(_DEST_DIR) && tar -xf -)
diff --git a/testing/mochitest/moz.build b/testing/mochitest/moz.build
index 71fa79181cf2..2ad6fa89a87a 100644
--- a/testing/mochitest/moz.build
+++ b/testing/mochitest/moz.build
@@ -26,12 +26,7 @@ MOCHITEST_MANIFESTS += [
 ]
 MOCHITEST_CHROME_MANIFESTS += ['chrome/chrome.ini']
 
-GENERATED_FILES += [
-    'automation.py',
-]
-
 TEST_HARNESS_FILES.testing.mochitest += [
-    '!automation.py',
     '/build/mobile/remoteautomation.py',
     '/build/pgo/server-locations.txt',
     '/build/sanitizers/lsan_suppressions.txt',