Leggo qui che

HTML5 added a “feature” to the web called hyperlink auditing. You can read the specification from the Web Hypertext Application Technology Working Group (WHATWG). Hyperlink auditing is added to a web page via
the ping attribute on an HTML anchor element (<a>), i.e., a link.

Notice that when you hover over the “Ping Me” link, you only see the href URL, you don’t see the ping URL, so you don’t even know that the attribute exists unless you look at the HTML page source. When you click the link, it loads the page http://lapcatsoftware.com/ as expected. But it also sends an HTTP POST request to http://underpassapp.com/ without any visible indication to the user.
You can only see it if you do a packet trace. It should come as no surprise that the primary usage of hyperlink auditing is for tracking of link clicks.

Firefox disables hyperlink auditing by default, as explained in a knowledge base article. You can see this if you open about:config and look at browser:send_pings.

Prior to Safari 12.1, you could disable hyperlink auditing with a hidden preference:

defaults write com.apple.Safari
com.apple.Safari.ContentPageGroupIdentifier.WebKit2HyperlinkAuditingEnabled
-bool false

Unfortunately, this no longer works in Safari 12.1. […]

I’ve been informed that chrome://flags#disable-hyperlink-auditing is now missing from the Google Chrome betas, even though it still exists in the current non-beta version. The flag was removed from the source code a little over a month ago.

In sintesi: quando clicchi su un link in pratica è come se cliccassi anche su un altro, senza poterlo sapere, a meno di non guardare il codice sorgente della pagina. In questo modo stai dicendo – a tua insaputa – ad un altro cosa stai facendo.

Firefox disabilita questa funzione per default; in Safari si poteva disabilitare ma adesso non più; in Chrome (e derivati, come Brave), per adesso si può disabilitare ma pare non si potrà più.

Bottom line: meno male che Mozilla c’è.