With the migration of the original CSS files from plain CSS to Less (a dynamic stylesheet language), we have introduced experimental Firefox support for the mobile framework. Firefox already supports the flexible box layout (albeit some exceptions compared to the WebKit implementation), so that we mostly had to adapt the vendor prefixes of the CSS properties. However, some bugs are still open, but you can already start testing the new feature right away, i.e. open it in Firefox.
With Less as the base for all CSS themes it started to get quite easy to extend existing themes and to create new ones. We added a new chapter to the manual, which describes how to use Less with qooxdoo. We would be happy to see people experiment with it, even to see new themes created by the community!