diff --git a/modules/macos_fsmonitor/manifests/init.pp b/modules/macos_fsmonitor/manifests/init.pp
new file mode 100644
index 000000000..84dd51d65
--- /dev/null
+++ b/modules/macos_fsmonitor/manifests/init.pp
@@ -0,0 +1,79 @@
+class macos_fsmonitor (
+  Boolean $enabled = true,
+) {
+  # Install the watchman package from S3
+  packages::macos_package_from_s3 { 'watchman.pkg':
+    private             => false,
+    os_version_specific => false,
+    type                => 'pkg',
+    require             => Exec['prepare_watchman_dir'], # Ensure the directory is created before the package is used.
+  }
+
+  # Step 1: Create the necessary directory
+  exec { 'prepare_watchman_dir':
+    command => 'sudo mkdir -p /usr/local/var/run/watchman',
+    creates => '/usr/local/var/run/watchman', # Ensures this is idempotent.
+    path    => ['/usr/bin', '/usr/local/bin'], # Ensure `mkdir` is found in the PATH.
+  }
+
+  # Step 2: Adjust ownership of the directory
+  exec { 'chown_watchman_dir':
+    command => 'sudo chown -R cltbld:staff /usr/local/var/run/watchman',
+    require => Exec['prepare_watchman_dir'], # Run only after the directory is created.
+    path    => ['/usr/bin', '/usr/local/bin'],
+  }
+
+  # Step 3: Codesign the `watchman` binary
+  exec { 'codesign_watchman':
+    command => 'sudo codesign --force --sign - /usr/local/bin/watchman',
+    onlyif  => '/bin/test -f /usr/local/bin/watchman', # Specify full path to 'test'.
+    require => Packages::Macos_package_from_s3['watchman.pkg'],
+    path    => ['/usr/bin', '/usr/local/bin', '/bin'],
+  }
+
+  # Step 4: Codesign the `watchmanctl` binary
+  exec { 'codesign_watchmanctl':
+    command => 'sudo codesign --force --sign - /usr/local/bin/watchmanctl',
+    onlyif  => '/bin/test -f /usr/local/bin/watchmanctl', # Specify full path to 'test'.
+    require => Packages::Macos_package_from_s3['watchman.pkg'],
+    path    => ['/usr/bin', '/usr/local/bin', '/bin'],
+  }
+
+  # Step 5: Manage `.hgrc` file for cltbld
+  file { '/Users/cltbld/.hgrc':
+    ensure  => file,
+    owner   => 'cltbld',
+    group   => 'staff',
+    mode    => '0644',
+    content => epp('macos_fsmonitor/hgrc.epp'), # Use a template for consistent content.
+    require => Exec['codesign_watchman'],
+  }
+
+  # Embedded Puppet Template (hgrc.epp)
+  # This template will look like this:
+  #
+  # <%# macos_fsmonitor/hgrc.epp %>
+  # [diff]
+  # git=True
+  # showfunc=True
+  # ignoreblanklines=True
+  #
+  # [ui]
+  # username = Mozilla Release Engineering <release@mozilla.com>
+  # traceback = True
+  #
+  # [extensions]
+  # share=
+  # rebase=
+  # mq=
+  # purge=
+  # robustcheckout=/usr/local/lib/hgext/robustcheckout.py
+  # sparse=
+  # fsmonitor =
+  #
+  # [fsmonitor]
+  # mode = paranoid
+  #
+  # [web]
+  # cacerts = /etc/mercurial/cacert.pem
+}
diff --git a/modules/roles_profiles/manifests/profiles/macos_fsmonitor.pp b/modules/roles_profiles/manifests/profiles/macos_fsmonitor.pp
new file mode 100644
index 000000000..ff021702b
--- /dev/null
+++ b/modules/roles_profiles/manifests/profiles/macos_fsmonitor.pp
@@ -0,0 +1,9 @@
+# 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/.
+
+class roles_profiles::profiles::macos_fsmonitor {
+  class { 'macos_fsmonitor':
+    enabled    => true,
+  }
+}
diff --git a/modules/roles_profiles/manifests/roles/gecko_t_osx_1400_r8_staging.pp b/modules/roles_profiles/manifests/roles/gecko_t_osx_1400_r8_staging.pp
index bf7e3c443..432c00ff5 100644
--- a/modules/roles_profiles/manifests/roles/gecko_t_osx_1400_r8_staging.pp
+++ b/modules/roles_profiles/manifests/roles/gecko_t_osx_1400_r8_staging.pp
@@ -7,6 +7,7 @@
   include roles_profiles::profiles::cltbld_user
   include roles_profiles::profiles::macos_bin_signer
   include roles_profiles::profiles::macos_directory_cleaner
+  include roles_profiles::profiles::macos_fsmonitor
   include roles_profiles::profiles::macos_gw_checker
   include roles_profiles::profiles::macos_people_remover
   include roles_profiles::profiles::macos_tcc_perms