While you're waiting for me to get round to releasing 0.5 beta, "GG" emailed me to say that he's created a repackaged version which works with Mozilla 1.4.
Doug has been doing some excellent work on Annozilla, and there is an experimental version available. This brings a lot of new functionality to Annozilla (including multiple server support). This version will form the basis of Annozilla 0.4.
This is the the Annozilla project, designed to view and create annotations associated with a web page, as defined by the W3C Annotea project. The idea is to store annotations as RDF on a server, using XPointer (or at least XPointer-like constructs) to identify the region of the document being annotated.
The intention of Annozilla is to use Mozilla's native facilities to manipulate annotation data - its built-in RDF handling to parse the annotations, and nsIXmlHttpRequest to submit data when creating annotations.
You can also see some screenshots - examples of Annozilla in action, and its integration with Mozilla. Currently there are screenshots for either the current released version, or the proposed new version which will be included in the forthcoming 0.4 release.
Please use the bug reporting mechanism or the mailing list to discuss Annozilla.