Firefox gets problems when 2,7 GB of memory is used by Firefox. Or more. Like 2,8 GB. It started when I read jpost.com with tens of tabs open. I don't remember how many. But I know there was more than 40. On the tab I that I was reading, the page turned completely black. Pitch black with nothing else, not even the Firefox interface. It was actually a pitch black shape that looked like a web page in shape. The blackness quickly disappeared and the page was normally readable again. But then it happened again - the page turned black again. The same page turns black happened again later. One of my browsing sessions had Firefox slow down so much that you could see scrolling happening when I used scrolling. Still another time I had 60 tabs open and Firefox worked completely fine without freezes, slowdowns, or black shapes. I could close Firefox by just pressing the red X in the title bar. Yesterday, I had 50 tabs open and I experienced a slowdown when I looked at the Breaking News headlines. The headlines would show slower than usual. The Breaking News headlines at jpost.com show the headlines a few words at a time until the headline is completely shown. Then the headline disappears and the next starts showing a few words at a time. And speed in general was not what you normally have with a computer that has 8 GB of memory. And a Core i5 processor. I opened two more tabs from the Breaking News section I had opened. After I opened a new window, Firefox froze. I had to close Firefox from the Task Manager by pressing End process. I had used Firefox for 6 hours without ever closing any of the tabs I had opened. In all of these cases, more than 40 tabs were open. In all of these cases, the slow down or freeze meant I had to use Task Manager and then press End process on the Processes tab. In all cases except the two I describe in the next paragraph, I never close any tabs after opening them. No problems have ever happened until Firefox started using 2,7 GB of memory. Until that point, everything is normal with no freezes or slowdowns. At two times, I tried to reduce memory usage by closing tabs. However, in both cases this would make Firefox freeze. In one of these cases, Firefox would show something bizarre: there would be about 7 tabs, and one of the tabs would be partly shown. Also, Firefox would show the busy cursor. Firefox did not show how many tabs I actually had. The second time, I tried to close the tabs by clicking Close other tabs in the menu that you get when right-click a tab. The tabs would close fine, but I remember that I opened Gmail and then I did this: I clicked on the Promotions tab. Instead of seeing the tab with the Emails, Firefox showed a busy cursor and the title bar said not responding. Firefox froze. The reason might be Adblock Plus memory usage. In Adblock Plus home page, developer Wladimir Palant writes in his blog about how Adblock Plus uses a lot of memory: https://adblockplus.org/blog/on-the-adblock-plus-memory-consumption .