There’s an extension for that: Status-4-Evar. I wrote about this handy extension back in January before Mozilla re-did things in Firefox 4 Beta 11 and 12 by putting connection status messages and link targets in an over-lay above the add-on bar. But for those of you who rather have this appear in the ‘status bar’ can do so with this extension. A couple notes, in the toolbars menu it will still be listed as add-on bar. Also, you can still hide/unhide the add-on status bar via CTRL+/. The extension is only for Firefox 4 and 4.2 (developmental/future Firefox 5).