QUOTE(doom9ra @ Dec 10 2015, 19:50)

1 single moment._.
when i even off monkey memory still leak._.
edit
yes,i know,that i need simply to relaunch Firefox,but i don't like it;(
1. Use incognito mode its slightly faster and does not drop speed all that much.
2. Go to about:memory and press the minimize memory usage button, it will give you back your top speed.
Btw 3.6->1.2 is very extreme there should be something wrong on your end, my speed drops are usually only 0.1~0.3t/s