Extension validation
I put the xul-extension through the Mozilla extention validator, in an effort to see what the Mozilla hosting of add-ons would think of the extension. they said that the install.rdf used an invalid version (specifically: 3.5.4), and only the following are allowed:
https://addons.mozilla.org/en-US/firefox/pages/appversions
It is a little odd you cannot specify this version. They do allow you to specify a minimum and maximum version that the add-on supports, or you can pull that information from the add-on itself. Using the automated method, i got this error, and the pull-down menus for manual specification do not have 3.5.4 allowed.
(from redmine: created on 2010-03-22, closed on 2010-04-05)