So as usual Firefox recently updated itself and starting banging on about how they are the most trusted, privacy aware browser etc etc.
But look carefully at the new version of Tiles (https://www.mozilla.org/en-US/firefox/tiles/) and you'll see that by default, FF is now tracking your browser history and using it to show you 'interesting and relevant' adverts, sorry, 'sponsored pages'. Hardly actions suitable for a browser going on about privacy.
Make sure you use the settings icon to switch Tiles back to classic (non-tracking) mode.