Firefox 4 will contain quite a bit of new features. One of the major areas which the Mozilla Corporation (MoCo) is looking to improve is the visual theme.

Throughout the last few months, MoCo’s Stephen Horlander has been publishing mockups and design ideas at his blog on the direction the Firefox team is taking with the theme. Overall, the theme is quite incredible. Its Windows design is one of the best of any browser on that platform, maybe of any application. The Mac platform design doesn’t quite hit the same level of beauty, but won’t stab you in the eye either.

Today, Horlander published new mockups on the proposed in-content UI. The Firefox team decided long ago to remove most dialogues and panels with in-content UI, meaning things like downloads, add-ons, and even preferences will be moved to the content window, instead of living in their own windows. It’s understandable that the Firefox team would want to go this direction. There has long been a problem with OS consistency in things like the preferences window and it has been nigh impossible to improve the situation.

However, screenshots like this one make me wonder about the long term OS integration goal. Firefox has always looked out of place on Mac. Making sweeping changes like this one will only push it further away from looking “right”, not closer.