What are third-party cookies? Why do browsers block third-party cookies?

// First-party cookie (allowed):
// Site example.com sets cookie for example.com ✅
 
// Third-party cookie (blocked):
// Site tracker.com tries to set cookie 
// when user is on example.com ❌

// When you're on site example.com
// And site example.com sets cookie
document.cookie = 'theme=dark'; // First-party cookie ✅
// This is allowed — site works with its own data

// When you're on site example.com
// But ad network tracker.com tries to set cookie
// through iframe or script on example.com
// This is third-party cookie ❌

// User visits different sites:
// news.com → tracker.com sets cookie ID123
// shop.com → tracker.com sees same cookie ID123
// blog.com → tracker.com sees ID123 again
 
// Result: tracker.com knows this is one person
// on different sites! This violates privacy! 🕵️

// ❌ Problem — cross-site tracking
// One tracker can collect data:
// - What you read
// - What you buy  
// - What you write
// - Where you go
 
// ✅ Solution — blocking third-party cookies
// Now tracker doesn't see you across sites

// In modern browsers:
// Chrome, Firefox, Safari block third-party cookies by default
 
// Before:
// tracker.com could set cookie on news.com
// Now:
// tracker.com CANNOT set cookie on news.com

// ✅ Sometimes useful:
// Login via Facebook/Google on different sites
// But now use other technologies (OAuth)

// ✅ Used before:
// Personalized advertising
// But now there are alternatives (FLoC, Topics API)

// Google develops new approaches:
// - FLoC (Federated Learning of Cohorts)
// - Topics API
// - And other privacy protection technologies

// ❌ Mistake — only third-party are blocked
document.cookie = 'mysite=value'; // First-party — works!
 
// ✅ Correct — only foreign cookies are blocked
// Cookies from other domains on your site

// ❌ Bad — relying on third-party cookies
// Soon they'll be gone completely!
 
// ✅ Good — use modern approaches
// First-party data, server solutions