in the 3D viewer (>18.0) the browserbar needs to be activated every time the program starts-up. I think that once this setting is selected, it should be persitent. this was the case in earlier versions of the viewer.
even after some research in my %appdata% i found a setting in the file sd_fluentui_layout.def which I thought would do the trick, but it seems to be overruled elsewhere. even though the same setting does change the lay-out in version 17.0 of the viewer.