--- a/hghooks/tests/test-prevent-wptsync-changes.t
+++ b/hghooks/tests/test-prevent-wptsync-changes.t
@@ -121,17 +121,16 @@ wptsync user can push changes to testing
   added 1 changesets with 2 changes to 2 files
 
 Test pushes to try
 
   $ cd ..
   $ rm -rf client
   $ hg init try
   $ configurehooks try
-  $ touch try/.hg/IS_FIREFOX_REPO
   $ hg -q clone try client
   $ cd client
   $ mkdir -p testing/web-platform/tests
   $ mkdir testing/web-platform/meta
   $ mkdir -p taskcluster/ci
   $ mkdir other
 
 

--- a/run-tests
+++ b/run-tests
@@ -15,16 +15,19 @@ import os
 import subprocess
 import sys
 
 # Mercurial's run-tests.py isn't meant to be loaded as a module. We do it
 # anyway.
 HERE = os.path.dirname(os.path.abspath(__file__))
 RUNTESTS = os.path.join(HERE, 'pylib', 'mercurial-support', 'run-tests.py')
 
+# By default the hgdev environment should use the same version of Mercurial
+# installed on the hg.mozilla.org servers.
+HGDEV_HG_VERSION = '4.2.3'
 
 if __name__ == '__main__':
     if 'VIRTUAL_ENV' not in os.environ:
         activate = os.path.join(HERE, 'venv', 'bin', 'activate_this.py')
         execfile(activate, dict(__file__=activate))
         sys.executable = os.path.join(HERE, 'venv', 'bin', 'python')
         os.environ['VIRTUAL_ENV'] = os.path.join(HERE, 'venv')
 
@@ -125,17 +128,22 @@ if __name__ == '__main__':
     os.environ['BUGZILLA_USERNAME'] = 'admin@example.com'
     os.environ['BUGZILLA_PASSWORD'] = 'password'
 
     orig_args = list(hg_harness_args)
 
     # Explicitly use our own HG from the virtualenv so other installs
     # on the system don't interfere.
     if not options.with_hg:
-        hg = os.path.join(os.path.dirname(sys.executable), 'hg')
+        # The hgdev env should use the same version on hg.m.o
+        if venv_name == 'hgdev':
+            hg = os.path.join(os.environ['VIRTUAL_ENV'], 'mercurials',
+                              HGDEV_HG_VERSION, 'bin', 'hg')
+        else:
+            hg = os.path.join(os.path.dirname(sys.executable), 'hg')
         hg_harness_args.extend(['--with-hg', hg])
 
     # Always produce an XUnit result file.
     hg_harness_args.extend(['--xunit',
         os.path.join(HERE, 'coverage', 'results.xml')])
 
     extensions = get_extensions()
     test_files = get_test_files(extensions, venv_name)