”The Enhanced Tile is displayed only for sites that would have appeared on a user's new tab page based on their browsing history. The improved image is supplied by the site or partner and can include a logo plus a rollover image. “ https://support.mozilla.org/en-US/kb/how-do-tiles-work-firefox#w_enhanced-tiles How—specifically—do websites supply this logo? What format is it? Where is it documented? From looking at the source, there does not seem to be a way for website owners to specify an image. https://mxr.mozilla.org/mozilla-central/source/browser/base/content/newtab/sites.js#156