Websites are automatically selected for the Tableau based on your browsing history. The set of websites on the Tableau can be changed in edit mode. To get there, open Tableau and select Tableau Settings in the context menu (or click the Set Tableau and background link).
A lock on a widget means the website is pinned to this position on the Tableau. The browser automatically changes the Tableau based on how often you visit various websites. If the lock is closed, the widget will always stay in the same place.
We are aware of this problem and are working on a solution.