Previously commented about this in bug 1627858 comment 64:

I think that ignores a larger problem, though - if the user is not using the Top Sites feature in about:home, why would they care about pins at all?

If bug 1623666 needs to happen, I think it needs to take into consideration whether Top Sites or about:home is enabled - and if not, pins and reordering of items on about:home is meaningless and it just needs to be based solely on historical data.

Since then, bug 1642177 was filed, where the user clearly has a pinned top site in their top sites feed, but is showing a site that has not been accessed in years.

Steps to reproduce:

1. Ensure Top Sites is enabled in about:preferences#privacy Address Bar
2. Ensure that there is at least one pinned tab in the top row of NTP
3. Either
   3a. Disable Top Sites in about:preferences#home
   OR
   3b. Disable Firefox Home for homepage/new windows or new tabs
4. Click in address bar

What happens:

I see a pinned top site in the address bar.

Expected result:

Since I am not using either NTP or the Top Sites feature in NTP, a list of customized top sites is meaningless to me, so I should see top sites solely based on frecency/history data, not based on customization in NTP Top Sites.