diff --git a/4.1.1-Calendar.md b/4.1.1-Calendar.md
index 96a62f3..51fdb7d 100644
--- a/4.1.1-Calendar.md
+++ b/4.1.1-Calendar.md
@@ -2,4 +2,4 @@ These options aren't really relevant if you're sending from an email such as you
 * `privacy.resistFingerprinting` When this is set to `true` your emails will be sent from a UTC timezone
   * If you do not want to have a UTC timezone then it is best you just comment out `privacy.resistFingerprinting`. If you set it to `false` you'll find that the DateTime picker in Calendar will not work and will loop back to -1 years with a date of 30/12/02. You'll also see this error in console 
   `JavaScript error: chrome://calendar/content/datetimepickers/datetimepickers.xml, line 1875: RangeError: date value is not finite in DateTimeFormat.format()`
-* `intl.regional_prefs.use_os_locales` When this option is set to `false` you won't see things according to your operating system's locale.
+* (Thunderbird <= v68) `intl.regional_prefs.use_os_locales` When this is set to `false` you won't see things according to your operating system's locale.