Why does Unity hide the menubars by default, instead of showing them in the free space across the panel?
One of the design goals of Unity is to reduce the clutter of the desktop, another is to use space more efficiently.
We hide the menu by default in Unity because the menu provides no useful information to which you can refer just by looking at it, but it puts a lot of detail on the screen which is visual clutter. So, we've taken the view that the menu is there if you need it (by moving the mouse to it or pressing Alt) but otherwise isn't in your view.
Many modern applications are doing without a menu altogether, so in our view, this is a step towards the future, and it will encourage application developers to think about their interfaces and make them more usable by design rather than depending on the crutch of a menu.
The conventions of FireFox and right click expediency particularly for organizing and deploying bookmarks directly contradicts Unity's conventions with no right click capability in the top menu bar.
It is laudable that when driving a VW you shouldn't have the cockpit of a 747, and ap. screen real estate should not be overwhelmed by perverse permuted excessive controls and menus, leaving no space for actual content but ... this should not be at the expense of real functionality.
There are ways to get around the bottlenecks but it is manually laborious. Our custom developed aps suffer by default in Unity from forced exile to the top bar and must be repatriated back to their originating window to restore functionality and visibility (as custom aps the visible existence of the menu provides mnemonic aid to obscure menu items and, however infrequently, they are essential and used).