Personas, now known as Lightweight Themes, don't need an add-on to work in Firefox. Firefox will remember 5 Lightweight Themes and allows you to change them in the Add-on Manager > Appearance tab.

I have read in this forum that some or all of the add-ons that extend the built-in "Personas" feature have quit working due to incompatibilities with Firefox 29-Plus versions, or even before Firefox 29 was released back in April. Check for an update for whatever add-ons you are suing to see if the developer/s of your add-ons have fixed it it or them.

Do you mean that you have a problem with an extension like Personas Plus that manages lightweight themes or is this about installing such a theme?

Previewing a lightweight theme (Persona) only works on sites that are white-listed via an allow exception, so make sure to have an allow exception for the addons.mozilla.org domain. You can see the permissions for the domain in the current tab here:

• Tools > Page Info > Permissions > [X] Install Add-ons

Note that your System Details List shows multiple Flash plugins.

• Shockwave Flash 15.0 r0
• Shockwave Flash 11.5 r502
• Shockwave Flash 11.3 r300

You can find the installation path of all plugins on the about:plugins page.

• http://kb.mozillazine.org/Issues_related_to_plugins#Identifying_installed_plugins

You can check the Flash player installation folder for multiple Flash player plugins and remove older version(s) of the plugin (NPSWF32) and possibly (re)install the latest Flash player.

• (32 bit Windows) C:\Windows\System32\Macromed\Flash\
• (64 bit Windows) C:\Windows\SysWOW64\Macromed\Flash\