I agree it was a good idea to get rid of the XUL-based UI and XUL addons. But I think allowing addons to apply some limited CSS changes to the new UI could be a

I agree it was a good idea to get rid of the XUL-based UI and XUL addons. But I think allowing addons to apply some limited CSS changes to the new UI could be a good compromise. It would be significantly less powerful than what could be done with XUL, but it would provide a more reasonable interface to go beyond simply changing colours and background images. I can acknowledge that there would be challenges creating such a feature in a way that is resistant to abuse, but I think it could allow the browser to regain a big competitive advantage at a fraction of the cost of the old implementation.