Did anyone notice after the update today (Jan 20) that the title bars in Chrome and Firefox have changed? There is a clear division between the tab bar area and the top window border. This did not exist before. Even loading themes into the browsers does not fix it.
This was part of a recent set of updates. The elementary GTK+ stylesheet was updated to make older (gtk2) applications look more like the new ones with the big header bars. Check their new blog post.