".onion available" is been displayed in an https onion site
An user reported that visiting SecureDrop onion site (https://secrdrop5wyphb5x.onion/) will show the purple pill (.onion available). And if you have enabled TBB to prioritize onions, the page will reload in loop.
Related: https://github.com/freedomofpress/securedrop.org/issues/698
Edited by Roger Dingledine