Bucket yourself as anonymous user who can see PagePreviews on Wikipedia

PagePreviewsBucketerForAnon.js

var sessId = 0,
    bucket = 'off';
    weightedBoolean = function getUserBucket( experiments, experimentGroupSize, sessionId ) {
      const control = experimentGroupSize / 2;
      if ( !experimentGroupSize ) {
        return 'on';
      }

	    return experiments.getBucket( {
		    name: 'ext.Popups.visibility',
		    enabled: true,
		    buckets: {
			    off: 1 - experimentGroupSize,
			    control,
			    on: control
		    }
	    }, sessionId );
    };

while( bucket != 'on' )	{
  sessId++;
  var samplingRate = mw.config.get( 'wgPopupsAnonsExperimentalGroupSize', 0 );
  bucket = weightedBoolean(
	  mw.experiments,
		mw.config.get( 'wgPopupsAnonsExperimentalGroupSize' ),
		sessId
	);
  console.log('For session ' + sessId + ' our bucket is ' + bucket);
}
mw.storage.session.store['mwuser-sessionId'] = sessId;

to disable it just run mw.storage.session.store['mwuser-sessionId'] = 0 and refresh the page