You will need to respond to the thread in order to get a chance to save to favorites. In other words, click on Reply and then post sth - even if it's "I just wanted to add this to my favorites." Now before you submit, scroll down past the graemlins and you will see the option
Add this thread to my favorites
Make sure that's checked before you Submit and the thread should now appear in your list of favorites on your home page.
HTH