Created attachment 953090 [details] Xorg log Hardware : LENOVO T61
Created attachment 953091 [details] lspci
Window manager is WindowMaker
I disabled HW acceleration in Firefox adding to prefs.js : user_pref("layers.acceleration.disabled", true); But the bug is still present.
I did a backup of the distribucion(f21) from the laptop(t61) to my desktop (i3-2120) and it doesn't show the bug. It should be something related to the HW(GM965).
Created attachment 953487 [details] lscpi-nn-desktop Running fine here: 00:02.0 VGA compatible controller [0300]: Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller [8086:0102] (rev 09)
It happens also in the Fedora-Live-Workstation ISO image.
ThinkPad T400 with "Core2 Duo P8600" and "00:02.0 VGA compatible controller [0300]: Intel Corporation Mobile 4 Series Chipset Integrated Graphics Controller [8086:2a42] (rev 07)" is also immune.
top command from a remote ssh session: PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 933 root 20 0 253772 26348 10616 R 98.8 0.9 4:17.24 Xorg.bin ^^^^
Created attachment 954719 [details] strace -o strace-f.txt -f -p 933
Created attachment 954721 [details] strace -o strace-f.txt -f
Also running fine here: T60 (Intel Core 2 T560) 00:02.0 VGA compatible controller [0300]: Intel Corporation Mobile 945GM/GMS, 943/940GML Express Integrated Graphics Controller [8086:27a2] (rev 03)
Fixed by: xorg-x11-drv-intel-2.99.916-3.20141117.fc21.x86_64 -thanks-
*** This bug has been marked as a duplicate of bug 1148493 ***