This problem occurs on BT’s Webmail system known as BT Mail found at: https://bt.com/email. (BT Yahoo is not affected)
When you add a new contact if there email address is over 30 characters long the browser will often freeze or severely slow down.
Please note this problem only occurs on BT’s webmail known as BT Mail, BT Yahoo’s Webmail system is NOT affected as far as I know, also email clients such as Outlook, Outlook Express, Windows Mail, Windows Live Mail, Incredimail, Eudora, Thunderbird, eM Client etc are not affected.