@JonJacobs,
Thanks for reaching out to us.
So there are two different modes for the “top-sites” widget that you are referring to (shown below) — one mode is “Top-sites”/“Frequently visited”, which populates based on sites that you visit most frequently. Note that you can still edit/remove sites from this list by hovering over the tile and clicking the “pencil” icon:
The other mode is “Favorites”, which is populated manually (entirely, I believe). You can swap between these modes by clicking the “three dots”/“more options” icon on the top-right corner of the widget:
Favorites can be added by clicking the Add site tile in the widget and just as above, sites can be removed and edited using the “pencil” icon when hovering over the tile. Lastly, you may click and drag in either mode to rearrange the tile order:
Hope this helps!