Mambo 4.5.5 is a maintenance release with following high-level updates:

(1) com_syndicate config parameter fixed
(2) RSS/SEO fixes
(3) IE7 fixes - Quirks mode and JSCookMenu update
(4) SQL injection fix in cancel edit functions

Mambo 4.5.5 is only for users of the 4.5.x series. Users of the 4.6.x series should NOT install this update. All 4.5.x users are encouraged to install 4.5.5 to avoid the possibility of your site visitors experiencing display issues in IE7.