From MozillaZine Knowledge Base

As of the 0.70 release, Nvu is based off Firefox 1.0. Hence users can easily install extensions in Nvu to enhance its functionality. Extensions for Nvu can be downloaded from the Official Mirror(temporary) and soon from Mozilla Update. Already available extensions are:

• about:config

• DOMInspector

• HTML Header

• Nvu Tutorial

• Venkman

You can also download extensions for Nvu from nvuext.mozdev.org