Using FX29 with vimperator, I added following js code in .vimperatorrc (maybe _vimperatorrc on windows) to show and hide the navigation bar by F2 key.
map <silent> <F2> :js toggle_navbar()<CR>
:js << EOF
function toggle_navbar() {
var nb = document.getElementById('nav-bar');
if (!nb)
return;
nb.style.visibility = (nb.style.visibility == '') ? 'collapse' : '';
nb.style.overflow = (nb.style.height == '') ? '' : 'hidden';
}
toggle_navbar();
EOF
I didn't test this without vimperator, however, I hope some add-ons like "Execute JS" or so can help your trial.