diff --git a/Makefile.in b/Makefile.in
index 012f69bebfc8f..845585fe40921 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -38,19 +38,12 @@ DIST_GARBAGE = config.cache config.log config.status* config-defs.h \
    .mozconfig.mk
 
 ifndef MOZ_PROFILE_USE
-# Automation builds should always have a new buildid, but for the sake of not
-# re-linking libxul on every incremental build we do not enforce this for
-# developer builds.  Tests always need a new buildid as well.
-ifneq (,$(MOZ_AUTOMATION)$(MOZ_BUILD_DATE)$(TEST_MOZBUILD))
+ifneq (mobile/android,$(MOZ_BUILD_APP))
 $(MDDEPDIR)/buildid.h.stub $(MDDEPDIR)/source-repo.h.stub: FORCE
 endif
-# Additionally, provide a dummy target during tests, because
-# faster/rules.mk will expect these targets to exist.
-ifdef TEST_MOZBUILD
 source-repo.h: $(MDDEPDIR)/source-repo.h.stub
 buildid.h: $(MDDEPDIR)/buildid.h.stub
 endif
-endif
 
 BUILD_BACKEND_FILES := $(addprefix backend.,$(addsuffix Backend,$(BUILD_BACKENDS)))
 
diff --git a/toolkit/library/gen_buildid.py b/toolkit/library/gen_buildid.py
new file mode 100644
index 0000000000000..67be70e03b965
--- /dev/null
+++ b/toolkit/library/gen_buildid.py
@@ -0,0 +1,34 @@
+# -*- 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/.
+
+
+from mozbuild.preprocessor import Preprocessor
+from io import StringIO
+import buildconfig
+import os
+
+
+def main(output, input_file):
+    with open(input_file) as fh:
+        if buildconfig.substs['EXPAND_LIBS_LIST_STYLE'] == 'linkerscript':
+            def cleanup(line):
+                assert line.startswith('INPUT("')
+                assert line.endswith('")')
+                return line[len('INPUT("'):-len('")')]
+
+            objs = [cleanup(l.strip()) for l in fh.readlines()]
+        else:
+            objs = [l.strip() for l in fh.readlines()]
+
+    pp = Preprocessor()
+    pp.out = StringIO()
+    pp.do_include(os.path.join(buildconfig.topobjdir, 'buildid.h'))
+    buildid = pp.context['MOZ_BUILDID']
+    output.write(
+        'extern const char gToolkitBuildID[] = "%s";' % buildid
+    )
+    return set(o for o in objs
+               if os.path.splitext(os.path.basename(o))[0] != 'buildid')
diff --git a/toolkit/library/moz.build b/toolkit/library/moz.build
index 0fed95365c7a0..d1c94504beac5 100644
--- a/toolkit/library/moz.build
+++ b/toolkit/library/moz.build
@@ -371,3 +371,20 @@ if CONFIG['COMPILE_ENVIRONMENT']:
 # This library is entirely composed of Rust code, and needs to come after
 # all the C++ code so any possible C++ -> Rust calls can be resolved.
 USE_LIBS += ['gkrust']
+
+# The buildid is refreshed on every (incremental) build. But we want to avoid
+# rebuilding libxul every time, so instead of having a source file that
+# #include's buildid.h, which would have a dependency on it, and that would
+# thus trigger make to rebuild everything, we generate a source with the
+# buildid hard coded in it. Then we make that source file depend on all the
+# objects files that constitute libxul, so that if any of the files linked into
+# libxul is rebuilt, we refresh the buildid and link it into libxul.
+SOURCES += ['!buildid.cpp']
+GENERATED_FILES += ['buildid.cpp']
+GENERATED_FILES['buildid.cpp'].script = 'gen_buildid.py'
+if CONFIG['MOZ_WIDGET_TOOLKIT'] in ('cocoa', 'uikit'):
+    libxul_list = 'XUL'
+else:
+    libxul_list = '%sxul_%s' % (
+        CONFIG['DLL_PREFIX'], CONFIG['DLL_SUFFIX'].lstrip('.'))
+GENERATED_FILES['buildid.cpp'].inputs = ['!%s.list' % libxul_list]
diff --git a/toolkit/xre/nsAppRunner.cpp b/toolkit/xre/nsAppRunner.cpp
index 020fe7ca31205..82fb05f714d20 100644
--- a/toolkit/xre/nsAppRunner.cpp
+++ b/toolkit/xre/nsAppRunner.cpp
@@ -253,10 +253,10 @@ static const char kPrefHealthReportUploadEnabled[] =
 int gArgc;
 char** gArgv;
 
-#include "buildid.h"
-
 static const char gToolkitVersion[] = NS_STRINGIFY(GRE_MILESTONE);
-static const char gToolkitBuildID[] = NS_STRINGIFY(MOZ_BUILDID);
+// The gToolkitBuildID global is defined to MOZ_BUILDID via gen_buildid.py
+// in toolkit/library. See related comment in toolkit/library/moz.build.
+extern const char gToolkitBuildID[];
 
 static nsIProfileLock* gProfileLock;