Comment 12 for bug 38131

I've the same problem, launching firefox on some page ( http://www.lesoir.be/ ). The computer slows down, Here is the result of top :
Tasks: 132 total, 2 running, 130 sleeping, 0 stopped, 0 zombie
Cpu(s): 90.0% us, 0.3% sy, 0.0% ni, 9.7% id, 0.0% wa, 0.0% hi, 0.0% si
Mem: 1028276k total, 844096k used, 184180k free, 36084k buffers
Swap: 1461904k total, 0k used, 1461904k free, 373752k cached

  PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
 5352 root 19 0 204m 26m 4748 R 85.2 2.7 2:57.95 Xorg
 7240 berti 16 0 254m 49m 25m S 2.7 4.9 0:02.95 firefox-bin
 5765 berti 15 0 142m 40m 20m S 2.0 4.0 0:59.21 konqueror

Killing firefox and everything gets back immediatly to the normal situation. I'm using an ati card with the open-source "ati" driver. This is an up-to-date dapper on a AMD64 machine.