One way to do it ...
When logged in (and that is important - doesn't apply if you haven't logged in as a registered user), and reading a thread, you have a "Thread Tools" drop down in the menu. Click "Subscribe to this thread" in that menu. This will "save" or "bookmark" a link to that particular thread for you.
Then, later when you want to go back to it, take a look under the Quick Links menu item, in the Miscellaneous group, you have a "Subscribed Threads" menu item. Click that and it shows all the threads you have subscribed to, and you can quickly and easily get back to ones you have "saved". Don't know if there is a limit to the number you can subscribe to, but would suggest keeping it to a small number of "really good ones".
Hope this answers your question.