Mail thread on plugin-futures: [https://mail.mozilla.org/private/plugin-futures/2010-January/001150.html https://mail.mozilla.org/private/plugin-futures/2010-January/001150.html]
In particular, Lloyd Hilaiel proposed an alternate approach where plugins would store everything in a standard filesystem based layout, so the UA itself can do the clearing. See [https://mail.mozilla.org/private/plugin-futures/2010-January/001156.html https://mail.mozilla.org/private/plugin-futures/2010-January/001156.html]
Flash Local Storage: [http://www.macromedia.com/support/documentation/en/flashplayer/help/help02.html http://www.macromedia.com/support/documentation/en/flashplayer/help/help02.html]
Firefox issue - clearing local storage with time range: [https://bugzilla.mozilla.org/show_bug.cgi?id=527667 https://bugzilla.mozilla.org/show_bug.cgi?id=527667]