How to add XUL elements on top of status bar?

I've been searching around for ways to add XUL elements on top of the statusbar. On previous findings, only <label> can be put there. But today, I found another way to put XUL elements on top of the status bar. Here are some sample codes:
<toolbox align="end" insertbefore="status-bar">
<toolbar id="nav-toolbar">
<textbox id="urlfield"/>
<toolbarbutton label="Send"/>
</toolbar>
</toolbox>