To add an item to your favorites, you need to be logged into your customer account. You can still click the "Like This Product" button, and it will direct you to log in. Once you log in, it directs you back to that product, so you can then like it, which adds it to your favorites for you to review later. If you wish to remove that item, simply click on the product and hit the "heart" icon again. This will remove it from your favorites.
If a fulfillment partner updates that product in the future, an email will notify you of those changes. Should you wish not to get emails for that particular product, you may unsubscribe from them under the product in your account. This is specific to each product. If you wish to unsubscribe from all product updates, you can do so at the top right corner.
When viewing products, you can also see how many other people have added it to their favorites because it will show a total within the "heart icon".