On the New Tab Page I have 16 pinned sites, half of them always displayed large favicons (from the TippyTop list or 'rich' icons provided by the sites, as I understand it) without me doing anything, while half showed screen captures with a small favicon in the bottom right corner. For the latter half I eventually found large icons on the web which I then set in the NTP 'Edit' for those sites.

Suddenly yesterday, one site that had always displayed a large icon without me specifying anything has changed to the small screen capture with small favicon overlay. There must be some way to change it back to the large icon that it's been displaying for years, but I don't know what that is. Can anyone help? How do you get Firefox to re-scan and find the TippyTop or rich icon again for a pinned top site?