Firefox version : 51.0.1 Add-on installed : uBlock, Quickjava, IDM CC https://s30.postimg.org/q5645rmq9/image.png Opened at least 8 tabs then firefox took around 700MB+ of RAM. Closed all the tabs but the memory consumption still didn't goes down, it's still at 700MB for no reason. And then firefox slowed down to a crawl, after that it become unusable (freeze / crash). My guess is FF garbage collection not working or not fast enough cleaning off the data / content of closed tabs. I found out that Chrome which is notorious for sucking off RAM (in old version), is actually much leaner now on RAM usage (Chrome latest version). It also crash much lesser than FF, and faster. Chrome really improving on something that really matter to end user like me, instead of adding a features which no one cares about. I really wish firefox was like that....