Long time ago,I have found the performance Bottleneck
Of fire is RAM,not CPU,at least for daily normal use like browser web.when I open more than 3 app like chrome videos music play store,the fire become so slow even get stuck, that's really bad.so the problem is It run out of RAM.it only has 1.7G ram for hd 10 and 1.4g for hd 7 or 8. That's really small today.here is solution I found , it's amazing efficient,really make your fire usable even you run many many apps simultaneously.
One word is "swap".
Swap can make you disk storage to be used as RAM,we know disk is slower than RAM,but as I have test, it's OK,you can do it. : )
First get your fire rooted
Next download a terminal I recommend termux,a powerful tool.
Open temux,now you can run many Linux command on you ,run following command:
dd if=/dev/zero of=swap bs=200m count=20
you will creat 200m*20 about 3.5G ram,also,it takes up the same amount storage,but it worth.
to check if you turn on swap run follow command:
You'll see you ram status include swap
if you dont ru su before,you dont need exit command beacause you are normal user
swap make big diff experience on you fire, now try it
i can run firefox snd chrome and many app at same time at a acceptable speed.amazing!!!