easy navigation of Gnome-menus by keyboard

The navigation of the Gnome-menus by keyboard is poor. Just the arrow-keys and
keys like home, end, pg-up and pg-down are supported.
It should also be possible to navigate by the main keys.
For example to launch the Firefox Web Browser that is located in the Internet
submenu the keysequence alt-f1, 'i', 'f' should suffice.
If there are multiple options beginning with the same letter the focus should be
cycled through each of them.
An even better way is to allow underscored characters that are used instead of
the leading character of the label of the option.
This functionality should be provided by the toolkit. But today's toolkit's
usually don't.
So this functionality should be provided by a toolkit abstraction layer.