Nutsmail is a commercialized assembly of customized skins wrapped around the mainstream Squirrelmail software. One of the Squirrelmail plugins we're using is 'avelsieve' which provide a web interface to the server-side sieve scripts. The latest version of this plugin uses Prototype JS -- but it doesn't bring prototype with it.
I've found mention of a work around that mentions adding Prototype to squirrelmail but I'm looking for more thorough instructions. URL to the avelsieve ticket which has the mention of adding prototype manually as a work around: http://email.uoa.gr/avelsieve/ticket/267