Well, it was going to happen. Mozilla upgrades Firefox to 3.5, Yeah! :-) ,but breaks the Google Notebook extension, booh :-(

So the usual work around is to change the maxVersion value in the extension as described on 'Google Operting System'

If you use a beta version of Firefox 3.5, here's a way to install the extension:

* save the extension to your computer: right-click and select "save link as".
* download 7-zip, an excellent open-source software for archiving files, and install it.
* right-click on the extension (google-notebook.xpi), click on "7-zip" and then on "open archive". Right-click on "install.rdf", select "Edit" and replace "3.0.*" with "3.5.*". Save the file, close Notepad and update the archive.
* now you can drag the .xpi file to your browser and install the extension.

I have done this and will most likely continue to maintain the modified version for as long as I continue to use Google Notebook and as long as the extension will work with Firefox.