--- a/testing/geckodriver/src/prefs.rs
+++ b/testing/geckodriver/src/prefs.rs
@@ -1,10 +1,17 @@
 use mozprofile::preferences::Pref;
 
+// ALL CHANGES TO THIS FILE MUST HAVE REVIEW FROM A GECKODRIVER PEER!
+//
+// The Marionette Python client is used out-of-tree with release
+// channel builds of Firefox.  Removing a preference from this file
+// will cause regressions, so please be careful and get review from
+// a Testing :: Marionette peer before you make any changes to this file.
+
 lazy_static! {
     pub static ref DEFAULT: [(&'static str, Pref); 80] = [
         // Make sure Shield doesn't hit the network.
         ("app.normandy.api_url", Pref::new("")),
 
         // Disable automatic downloading of new releases
         ("app.update.auto", Pref::new(false)),
 

--- a/testing/marionette/client/marionette_driver/geckoinstance.py
+++ b/testing/marionette/client/marionette_driver/geckoinstance.py
@@ -17,16 +17,24 @@ import mozversion
 from mozdevice import DMError
 from mozprofile import Profile
 from mozrunner import Runner, FennecEmulatorRunner
 from six import reraise
 
 from . import errors
 
 
+# ALL CHANGES TO THIS FILE MUST HAVE REVIEW FROM A MARIONETTE PEER!
+#
+# The Marionette Python client is used out-of-tree with release
+# channel builds of Firefox.  Removing a preference from this file
+# will cause regressions, so please be careful and get review from
+# a Testing :: Marionette peer before you make any changes to this file.
+
+
 class GeckoInstance(object):
     required_prefs = {
         # Make sure Shield doesn't hit the network.
         "app.normandy.api_url": "",
 
         # Increase the APZ content response timeout in tests to 1 minute.
         # This is to accommodate the fact that test environments tends to be slower
         # than production environments (with the b2g emulator being the slowest of them