Hello! Already a long time i have strange problem in Firefox (even in the current v56.0.2 version) under Windows 7 & Linux (Ubuntu 16.04 LTE). Problem occurs every day in many times. Manifestations: when i have browsing even with 1-2 tabs the firefox begins to eat one core of CPU. If computer has 8 cores - a firefox eats 13%. If OS is Ubuntu - i see 100% in top command (100% there is one core load). Sometime Firefox hangs up, sometime i can do "Quit". But! After quiting i see firefox process to be eating same volume CPU (one core only). If i start again Firefox i see warning that the firefox is running. To repair this problem i do: in Windows i kill process by manually through Task manager, in Ubuntu i do "killall -HUP firefox". When i start firefox again after a few time problem comes to me again... Same problem exists a long time. I saw this in 54, 55 versions of Firefox. This problem is aggravated by the fact that it is not reported through crash reports (about:crashes) because it's not crash for firefox itself... This problem may be diagnosted only by Night buildes but i tried to install Night build and it very buggy but i should work... So i cannot catch a reasons of this bug. I even tried to run Safe mode many times but problem comes to again and again. It not related with amount of opened tabs! I see it with only one (!) empty tab! I tried to delete Firefox account and did the new account for synchronization. It didn't help to me in anyway... I don't know what happens with Firefox but it happens and it is there! I even think about a hidden mining of cryptocurrencies installed to all releases of Firefox. I cannot other imagine why it regulary is there and not to be fixed. And i don't see many topics about this but it definitely exists! And i don't know what can i do :( I disabled many not-important for me add-ons but problem exists. Please write to here anybody who sees same problem regulary! Best regards, Alexey