We have a new feature, discovered by the estimable Brighternow.
If you prefer not to have sticky threads, now known as Announcements, at the top of your feed, go to the main discussion list, hover your cursor just to the left of the 'favorite' star to the right of each Announcement thread and a cog wheel should appear. Click on it and select Dismiss. That thread will now behave like a normal thread on your feed and only pop to the top when it has a new post. You will still see the Announcement tag under it, but it will not be sticky.
As far as I have been able to discover so far, this might not be reversible. The cogwheel seems to go away after you dismiss the announcement.
But you can safely try it with this one, which is just an announcement for you to play with.