I remember this line from a cowboy movie about gold prospecting in the Wild Wild West as the barmaid kept her tips in her bra: "There's gold in them hills."
You don't need to be signed in or even have an account. They know exactly what is going on at sites which embed their code.
From XAi
Facebook tracks your activities on third-party websites through embedded content like videos, "Like" buttons, or other social plugins using a combination of code and tracking mechanisms. Here's how it works:
Embedded Code (Social Plugins): When a website embeds Facebook content (e.g., a video or a "Like" button), it includes a snippet of JavaScript code from Facebook, such as the Facebook SDK or iframe-based plugins. This code loads content directly from Facebook’s servers and establishes a connection between your browser and Facebook.
Cookies and Tracking Pixels:
Cookies: If you’re logged into Facebook or have previously interacted with their services, cookies (like the fr or datr cookie) stored in your browser can identify you across sites. These cookies link your activity on the third-party site to your Facebook profile.
Facebook Pixel: Many websites use the Facebook Pixel, a piece of code that tracks user actions (e.g., page views, clicks, or purchases). If the site you’re visiting has the Pixel installed, it sends data about your behavior back to Facebook, even if you don’t interact with the embedded content.
Browser Fingerprinting and Identifiers: Even if you’re not logged into Facebook, the embedded code can collect data like your IP address, browser type, device information, or other unique identifiers to create a "fingerprint" of your activity. This can sometimes be linked to your Facebook profile later if you log in.
Data Collected: The embedded code can track:
The URL of the page you’re visiting.
The time spent on the page.
Interactions with Facebook content (e.g., playing a video or clicking "Like").
Other actions on the site if the Pixel or similar tools are implemented.
Cross-Site Tracking: When you visit a site with Facebook’s code, it can communicate with Facebook’s servers, which may link your activity to your Facebook account (if logged in) or a shadow profile (if not logged in). This data is used for targeted advertising and analytics.
Mitigation Options:
Log Out: Logging out of Facebook reduces direct tracking tied to your account.
Block Cookies: Use browser settings or extensions to block third-party cookies.
Privacy Tools: Use ad blockers or privacy-focused browsers (e.g., Firefox with enhanced tracking protection) to limit tracking.
Opt-Out: Adjust your Facebook ad settings or use tools like the Digital Advertising Alliance’s opt-out page.
Incognito Mode: While not foolproof, private browsing can reduce cookie-based tracking.
This tracking is part of Facebook’s broader advertising ecosystem, which collects data to build detailed user profiles for personalized ads. For more control, check your browser’s privacy settings or review Facebook’s off-site activity settings.