playlist-extension/content_scripts/content.js

(function() {
  console.log('Content script loaded');
  
  /**
   * Check if the current URL matches the pattern
   * @param {string} urlPattern - URL pattern to match
   * @returns {boolean} - Whether the current URL matches the pattern
   */
  function matchesUrlPattern(urlPattern) {
    const regex = new RegExp(urlPattern);
    return regex.test(window.location.href);
  }

  /**
   * Function to inject and execute custom code on the page
   */
  function injectCustomCode() {
    console.log('Custom code injected into the page');
    
    // Example: Add a banner to the top of the page
    const banner = document.createElement('div');
    banner.textContent = 'This page has been modified by My Firefox Extension';
    banner.style.cssText = 'position: fixed; top: 0; left: 0; width: 100%; background: #ffcc00; padding: 10px; text-align: center; z-index: 9999;';
    document.body.prepend(banner);
    
    // You can add more functionality here
  }

  // Listen for messages from the popup or background script
  browser.runtime.onMessage.addListener((message) => {
    if (message.command === 'injectCode') {
      injectCustomCode();
      return Promise.resolve({status: 'Injection completed'});
    }
  });
  
  // Check if we should automatically inject code based on URL
  if (matchesUrlPattern('example\\.com')) {
    injectCustomCode();
  }
})();