Firefox comes with default support for themes and Personas, themes allow the user to add a complete visual theme to Firefox (with modified scrollbars, dialogs, drop-down, etc), while Personas present themselves as partial themes, allowing the user to modify only certain aspects of Firefox (such as the toolbar).
Weeks ago, the LibreOffice developers announced the upcoming support for Personas in LibreOffice 4.0 release candidate 1, support designed with Firefox Personas in mind.