Is there a way to increase the number of tiles?
If not, please add that option.
In basic Firefox you can change browser.newtabpage.columns and browser.newtabpage.rows in about:config to increase the number of tiles, which I find very usefull. It gives you a quick acces in a new tab to the most visited pages, being far more useful than the ones from history, which are more a 1-time visit like articles, news, etc.