[Notes]: - The issue is not reproducible if you import history from another browser. [Affected versions]: - Firefox 57 and up [Affected Platforms]: - All Windows - All Mac - All Linux [Prerequisites]: - On a new profile sign in to sync with an account that has enough history and bookmarks to populate the "Top Sites" area. [Steps to reproduce]: 1. Open the browser with the profiles from prerequisites. 2. Pin a Top Site and open it in multiple new tabs. 3. Restart the browser. 4. Unpin the Top Site pinned at step 2 and observe its behavior. [Expected result]: - The Top Site stays in the same place. [Actual result]: - The Top Site disappears or it is moved towards the back in the "Top Sites" area. [Additional Notes]: - Attached a screen recording of the issue.

Here is the screen recording of the issue: https://goo.gl/AV7fsQ