MPL stands for Mozilla Public License. NPL (Netscape Public
License) gives Netscape the privilege of re-licensing the
modifications that is made to the software, they can take those
modifications private, improve them and refuse to give the result.
Netscape created the MPL, to address this concern. The MPL is much
like the NPL but does not contain the clause that allows Netscape
to re-license the modifications made.In short, The NPL and MPL
allows you to take modifications private.