You can create extra toolbars to get extra space via "View > Toolbars > Customize" to see more of the Persona (lightweight theme).
You have to put something on a toolbar (drag a Space item onto it) before closing the Customize window because empty toolbars are automatically removed.

• https://support.mozilla.org/kb/How+to+customize+the+toolbar

Note that you won't be able to do this anymore once the Australis code lands on the release channel (the Australis code will probably land in Firefox 29).

• http://www.ghacks.net/2014/01/31/mozilla-decides-uplift-australis-firefox-aurora/

I have been struggling to find a way to see my entire persona/theme. I went to add on and got the "Lighterweight Themes" for Australis 1.0.1 and was disappointed for last few days, until I clicked on "OPTIONS", located on the right of the "Lighterweight Themes" for Australis 1.0.1 Add On, next to the "Disable" & "Remove". I then scrolled down to "Add Empty Space Around Tabs". You have 2 choices. The first choice is "Top (pixels). I started to increase up to 70 and can now see my entire Persona/Theme!!! Frik'n Awesome!!!