To quote Jamie Hyneman, “Whoops!”
In posting the 0.2.* series of XUL Widgets XPI’s, I listed incorrect information in the install.rdf and update.rdf files. This mandates posting a new XUL Widgets 0.3.0 XPI & XULRunner series.
No new functionality, but you will find XULRunner 0.2 will not receive any future updates. So please uninstall it before installing version 0.3. XUL Widgets version 0.3 should be available in 24 hours or less.
UPDATE: Another well-formedness error bit me, install.rdf. 0.3.1 released now.
UPDATE 2 : Note to self: chrome.manifest is useful. 0.3.2 released.