Browser cookies can be used to store small amounts of data on the client-side (i.e. the user's browser), and they can be used for a variety of purposes, including:

1. Session management: Cookies can be used to maintain session information, such as user authentication tokens, across multiple requests.

2. Personalization: Cookies can be used to store user preferences or settings, such as language, theme, or font size.

3. Tracking: Cookies can be used to track user behavior, such as page views or clicks, for analytics or advertising purposes.

4. E-commerce: Cookies can be used to store items in a user's shopping cart or to remember user details during the checkout process.

5. Performance: Cookies can be used to improve website performance by caching frequently used data or settings.

6. Security: Cookies can be used to implement security features, such as CSRF protection or rate limiting.

It's important to note that cookies have some limitations and potential drawbacks, such as privacy concerns, cross-site scripting vulnerabilities, and size limitations. As a result, it's important to use cookies carefully and responsibly, and to consider alternative storage mechanisms when necessary.

Here's an updated example that uses the newer localStorage API instead of cookies to store the bookmarked page:

<script>
  function setBookmark() {
    // Save the current page URL to localStorage
    localStorage.setItem("bookmark", window.location.href);
    alert("Page bookmarked!");
  }

  // Check if the bookmark is saved in localStorage, and display a message to the user
  var bookmark = localStorage.getItem("bookmark");
  if (bookmark) {
    alert("You have bookmarked this page: " + bookmark);
  }
</script>

<a href="#" onclick="setBookmark()">Bookmark this page</a>

In this example, we use the localStorage API to save the bookmarked page URL instead of using cookies. The localStorage API provides a simple way to store data on the user's browser that persists even after they close the browser window.

We define a setBookmark() function that saves the current page URL to localStorage and displays an alert to confirm that the page has been bookmarked. We also check if the bookmark is already saved in localStorage when the page loads, and display a message to the user if it is.

The link to bookmark the page calls the setBookmark() function when clicked.

Note that this example uses the localStorage API, which is supported by most modern browsers. However, if you need to support older browsers, you may need to use a polyfill or fallback approach that uses cookies or other storage mechanisms.

<script>
  function setBookmark() {
    // Set a cookie with the current page URL
    document.cookie = "bookmark=" + encodeURIComponent(window.location.href);
    alert("Page bookmarked!");
  }
  
  function getBookmark() {
    // Get the value of the bookmark cookie
    var cookies = document.cookie.split(';');
    for (var i = 0; i < cookies.length; i++) {
      var cookie = cookies[i].trim();
      if (cookie.indexOf('bookmark=') == 0) {
        return decodeURIComponent(cookie.substring('bookmark='.length));
      }
    }
    return null;
  }
  
  // Check if the bookmark cookie is set, and display a message to the user
  var bookmark = getBookmark();
  if (bookmark) {
    alert("You have bookmarked this page: " + bookmark);
  }
</script>

<a href="#" onclick="setBookmark()">Bookmark this page</a>

In this example, we define two functions: setBookmark() and getBookmark(). setBookmark() sets a cookie with the current page URL when called, and getBookmark() retrieves the URL from the cookie.

We then create a link that calls the setBookmark() function when clicked. When the link is clicked, the cookie is set and an alert is displayed to confirm that the page has been bookmarked.

Finally, we check if the bookmark cookie is set when the page loads, and display a message to the user if it is.

Note that this example uses a simple approach to store the bookmark URL in a cookie, which may not be suitable for all use cases. You may want to consider other approaches, such as using browser storage or server-side storage, depending on your needs.

<style>
  .floating-ad {
    position: fixed;
    bottom: 20px;
    right: 20px;
    background-color: #fff;
    border: 1px solid #ddd;
    padding: 10px;
    display: none;
  }
</style>

<div class="floating-ad">
  <a href="#" target="_blank">
    <img src="/ad-1.png" alt="Ad 1">
  </a>
</div>

<script>
  var ads = [
    {
      imageUrl: 'ad-1.png',
      linkUrl: 'https://example.com/special-offer-1'
    },
    {
      imageUrl: 'ad-2.png',
      linkUrl: 'https://example.com/special-offer-2'
    },
    {
      imageUrl: 'ad-3.png',
      linkUrl: 'https://example.com/special-offer-3'
    }
    // Add more ads here as needed
  ];
  
  var randomAdIndex = Math.floor(Math.random() * ads.length);
  var ad = ads[randomAdIndex];
  
  var randomTime = Math.floor(Math.random() * 60000) + 60000; // Random interval between 1 and 2 minutes
  setTimeout(function() {
    var adElement = document.querySelector('.floating-ad');
    adElement.querySelector('img').src = ad.imageUrl;
    adElement.querySelector('a').href = ad.linkUrl;
    adElement.style.display = 'block';
  }, randomTime);
</script>

In this example, we have an array of ads that includes the URLs of the image and the link for each ad. We then use JavaScript to randomly select an ad from the array, and set the image and link for that ad in the floating ad element.

You can add more ads to the array as needed, and customize the ad image and link URLs to match your website's offers. Note that this is a basic example and you may want to consider other factors, such as the size and placement of the ad, to optimize its effectiveness.