All items may be placed and grouped freely on PrefBar's bar. The bar itself may be moved using the browser built-in "toolbar customize" feature to anywhere you like (even in foreign toolbars, next to the menubar, ...).
A full list of built-in buttons is available here: http://prefbar.tuxfamily.org/help/buttons.html
You may create your own buttons (simple documentation included) or download more buttons from this page: http://prefbar.tuxfamily.org/buttons.html
For bug reports, please use the Bugzilla installation here: http://prefbar.tuxfamily.org/bugs.html