Zevahim 61: The Fire Never Left the Altar - Unless It Did?

When the Tabernacle was in Shilo, the altar seems to have been made of stones, and not the copper that Moshe made. But if that's the case, how was there unceasing use of the same altar from Moshe to Shlomo (Moses to Solomon)? The Gemara, of course, attempts to resolve that contradiction to the satisfaction of both claims (no ceasing of the fire on the altar from Moses to Solomon and the ostensibly stone altar). Also, the size of the altar in the Second Temple (long after Solomon's altar in the First Temple), based on a mishnah in Middot. Plus, why the size was increased.