How to disable P3P in Joomla
Anyway, Joomla implemented it and by default provides contradicting P3P tags (which may even be dangerous and put you at risk, as you publish wrong (summary) policy information – people, and lawyers, may actually take you by your word/P3P tags) [as discussed here].
To disable them (or – same places for configuration of course):
In Joomla >= 1.6:
Go into your administration panel,
into extensions -> plugins,
search for p3p
disable the System – P3P Policy plugin (or configure, if you want)
In Joomla 1.5:
Actually, it is hard-coded. Bad idea!
libraries/joomla/session/session.php, line 426; comment it out (or configure, if you want) [path-source, verified]