Originally Posted by IBobi

This change was deliberate -- now you can tap the thread title to go to the first post, or tap the "Last Post" arrow underneath the thread title and go to the most recent post. I realize that's not exactly "go to first unread" but our data shows that this is closer to what most forum users wanted out of mobile browsing.

You may also tap the thread title, which takes you to the first post, and below the title once you are in the thread you'll see a link to "View First Unread" which disappears after you've viewed the thread again.