Plugin Sample code license?

Neil Marshall <[email protected]>
Newsgroups gmane.comp.mozilla.license
Organization Another Netscape Collabra Server User
Message-ID <[email protected]>
I'm building a plugin for firefox and all the sample code has a NPL/GPL 
2/LPL 2.1 license at the top.

Does this mean I have to open any of my plugin to the public if I base 
it off of the sample code?  Or being NPL, does it allow me to keep it 
closed source?
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