Edit: The problem has nothing to do with Safari, Firefox or Flash, It occurs without those apps beeing running! I've had this problem for a couple of months now. When I activate Flash and visit any webpage with flash content it's just a matter of time til network traffic is blocked. On some occations the mouse pointer starts lagging, flash movie even in low resolution starts lagging, opening activity monitor shows low usage of CPU and HD, no problem there. I'm connected via cable and sometimes when this happens, switching to WiFi will help for a short while, then traffic is blocket over this interface too. Opening the network settigs dialogue will show network connection is OK. I have tried renewing DHCP address, unplugging the cable, stopping and starting the connection, nothing helps but restarting the computer. The problem is the same whether I use Safari or Firefox, both up to date. I have an old macbook, white late 2006 i think, OS X 10.7.5, of course it's an old computer, but I won't settle for the "hardware outdated" answer. There is some other cause making network traffic getting blocked. I've searched the internet and found nothing on this problem, any ideas?