Hushmail is NOT secure or private [1] . The sentence "even an employee with access to their servers can’t get the actual data of the email" is false. Do not use.

Edit: Adblock Plus allows certain "acceptable ads" (read: companies pay Adblock Plus to get whitelisted) and this feature is turn on by default. Use the fork Adblock Edge [2]

[1] http://www.wired.com/threatlevel/2007/11/encrypted-e-mai/

[2] https://addons.mozilla.org/en-US/firefox/addon/adblock-edge/