web site that ask you login and password.
when you log , the website simulate a firefox browser with your bookmarks, organise as a toolbar like firefox bookmark toolbar folder.
The simulated browser allow you to surf as a normal browser, and to save bookmark with drag and drop functionality of firefox bookmark toolbar folder.
No client to be downloaded, it needs to be transparent to the user.
once he log in , he needs to be in front of a exact replic of firefox but with his bookmarks appearing in a firefox bookmark toolbar.
Obviously all the bookmark are saved on he web site side, secured access (login password) and synchronised when any change from the user (add, remove..) is activated.