Manual:$wgExtendedLoginCookieExpiration/ja

詳細
The purpose of this cookie is to allow having a different (usually longer, but this is not enforced) duration for "" login-related cookies. This means you can e.g. set the standard cookie duration (widely used for MW cookies) to 30 days, but set the "" duration to a year.

値の意味は以下の通り:
 * null - MW は代わりに の値に従います.
 * 正の整数 - セッションの「」期間 (秒単位).
 * 0 - ブラウザーを閉じた際にセッションの「」期間が終了します.