Take a look at:
http://www.mozilla.org/MPL/relicensing-faq.html
Basically, they used to be MPL, and are attempting to turn into MPL/NPL/GPL tri-license. Changing the license for an open-source project is quite tricky, so they aren't done.
As a general question, though, the KDE frontend would not have been enough to change the license, as long as everything was done right.