--- a/toolkit/moz.configure
+++ b/toolkit/moz.configure
@@ -1206,8 +1206,21 @@ with only_when(has_elfhack):
 @depends(check_build_environment)
 def idl_roots(build_env):
     return namespace(ipdl_root=os.path.join(build_env.topobjdir, 'ipc', 'ipdl'),
                      webidl_root=os.path.join(build_env.topobjdir,
                                               'dom', 'bindings'))
 
 set_config('WEBIDL_ROOT', idl_roots.webidl_root)
 set_config('IPDL_ROOT', idl_roots.ipdl_root)
+
+# Proxy bypass protection
+# ==============================================================
+
+option('--enable-proxy-bypass-protection',
+       help='Prevent suspected or confirmed proxy bypasses')
+
+@depends_if('--enable-proxy-bypass-protection')
+def proxy_bypass_protection(_):
+    return True
+
+set_config('MOZ_PROXY_BYPASS_PROTECTION', proxy_bypass_protection)
+set_define('MOZ_PROXY_BYPASS_PROTECTION', proxy_bypass_protection)