The site can signal, either via server headers or meta tags, whether to send or withhold referrers. Adding <meta name="referrer" content="never"> will prevent

The site can signal, either via server headers or meta tags, whether to send or withhold referrers. Adding <meta name="referrer" content="never"> will prevent referrers from being sent, whilst <meta name="referrer" content="always"> will ensure they're sent whether linking to HTTP or HTTPS. The user can of course override these if so desired - see the extensions linked to by many other commenters.