This is a regular patch release, which includes many bugfixes but no feature enhancements. It is meant to be backwards compatible to qooxdoo 1.4.1 and 1.4. Nothing needs to be changed in the JavaScript code of your existing apps, if they are based on the previous 1.4.x releases.
See the corresponding bugzilla query for over 120 issues resolved for qooxdoo 1.4.2.