I have only recently bought this particular MacBook Pro so I am still learning how to get the best out of it. One thing I have noticed on several Macs is that Firefox is a heavy power user. The latest version has a thing called Task Manager (not to be confused with Windows Task Manager) which lets you see which tabs are using most power. In may case that appears to be Amazon so I no longer have any Amazon tabs open which might be beneficial in other respects as well. Worth checking, if your browser permits, which tabs/pages are using the power.