This behaviour comes from Windows and MacOS where the tab key was used to move between interface elements. The first browsers were built with the same widget to

This behaviour comes from Windows and MacOS where the tab key was used to move between interface elements. The first browsers were built with the same widget toolkit that the operating systems provided. From the UI perspective of the these interfaces, the tab key is doing exactly what it is supposed to do and making it do something else would break user expectations. It annoys me too, but there is a reason for it.