You need to block the standard prototype.js, prototype_improvements.js and behaviour.js files in order to make both elements work together. Between the
Requirements::javascript( "flickrservice/js/prototype.js" );
Requirements::javascript( "flickrservice/js/scriptaculous.js" );
Requirements::javascript( "flickrservice/js/lightbox.js" );
and
Requirements::css("flickrservice/css/lightbox.css");
Copy and paste the below section to block the files. I have included comments to briefly explain what and why etc.
You might need to check the locations for your version of SilverStripe etc.
// Block the following conflicting JS files to enable Full Text Search AND Lightbox.
// These two files are responsible for stopping the Lightbox from working.
Requirements::block("sapphire/thirdparty/prototype/prototype.js");
Requirements::block("sapphire/javascript/prototype_improvements.js");
// This file MUST be blocked to ensure the Full Text Search continues to work.
Requirements::block("sapphire/thirdparty/behaviour/behaviour.js");
Hope this helps if you haven't fixed it before now! ;o)