Freezes computer using a lot CPU

steps to reproduce: start firefox (7.0), open page saunalahti.fi

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: xorg 1:7.6+7ubuntu7
ProcVersionSignature: Ubuntu 3.0.0-11.17-generic 3.0.4
Uname: Linux 3.0.0-11-generic i686
ApportVersion: 1.22.1-0ubuntu2
Architecture: i386
Date: Tue Sep 20 21:59:54 2011
InstallationMedia: Xubuntu 11.10 "Oneiric Ocelot" - Beta i386 (20110901)
ProcEnviron:
 LANGUAGE=en_US:en
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: xorg
UpgradeStatus: No upgrade log present (probably fresh install)
---
ApportVersion: 1.22.1-0ubuntu2
Architecture: i386
DistroRelease: Ubuntu 11.10
InstallationMedia: Xubuntu 11.10 "Oneiric Ocelot" - Beta i386 (20110901)
Package: xorg 1:7.6+7ubuntu7
PackageArchitecture: i386
ProcEnviron:
 LANGUAGE=en_US:en
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 3.0.0-11.17-generic 3.0.4
Tags: oneiric
Uname: Linux 3.0.0-11-generic i686
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm admin cdrom dialout lpadmin plugdev sambashare
---
ApportVersion: 1.23-0ubuntu1
Architecture: i386
DistroRelease: Ubuntu 11.10
InstallationMedia: Xubuntu 11.10 "Oneiric Ocelot" - Beta i386 (20110901)
Package: xorg 1:7.6+7ubuntu7
PackageArchitecture: i386
ProcEnviron:
 LANGUAGE=en_US:en
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 3.0.0-11.18-generic 3.0.4
Tags: oneiric
Uname: Linux 3.0.0-11-generic i686
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm admin cdrom dialout lpadmin plugdev sambashare
---
ApportVersion: 1.23-0ubuntu1
Architecture: i386
CompizPlugins: No value set for `/apps/compiz-1/general/screen0/options/active_plugins'
CompositorRunning: None
DistUpgraded: Fresh install
DistroCodename: oneiric
DistroRelease: Ubuntu 11.10
DistroVariant: ubuntu
ExtraDebuggingInterest: Yes, whatever it takes to get this fixed in Ubuntu
GraphicsCard:
 nVidia Corporation NV17 [GeForce4 MX 420] [10de:0172] (rev a3) (prog-if 00 [VGA controller])
   Subsystem: Micro-Star International Co., Ltd. Device [1462:8781]
InstallationMedia: Xubuntu 11.10 "Oneiric Ocelot" - Beta i386 (20110901)
Lsusb:
 Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
 Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
 Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
 Bus 002 Device 002: ID 0a81:0205 Chesen Electronics Corp. PS/2 Keyboard+Mouse Adapter
 Bus 003 Device 002: ID 046d:c00e Logitech, Inc. M-BJ58/M-BJ69 Optical Wheel Mouse
Package: xorg 1:7.6+7ubuntu7
PackageArchitecture: i386
ProcEnviron:
 LANGUAGE=en_US:en
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.0.0-11-generic root=UUID=5009f2ca-a80f-41f4-9717-85795485bed9 ro quiet splash vt.handoff=7
ProcVersionSignature: Ubuntu 3.0.0-11.18-generic 3.0.4
Tags: oneiric ubuntu
Uname: Linux 3.0.0-11-generic i686
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm admin cdrom dialout lpadmin plugdev sambashare
dmi.bios.date: 04/25/2005
dmi.bios.vendor: Phoenix Technologies, LTD
dmi.bios.version: 6.00 PG
dmi.board.name: MS-7051
dmi.board.vendor: MICRO-STAR INTERNATIONAL CO., LTD
dmi.chassis.type: 3
dmi.modalias: dmi:bvnPhoenixTechnologies,LTD:bvr6.00PG:bd04/25/2005:svn:pn:pvr:rvnMICRO-STARINTERNATIONALCO.,LTD:rnMS-7051:rvr:cvn:ct3:cvr:
version.compiz: compiz N/A
version.libdrm2: libdrm2 2.4.26-1ubuntu1
version.libgl1-mesa-dri: libgl1-mesa-dri 7.11-0ubuntu3
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 7.11-0ubuntu3
version.xserver-xorg: xserver-xorg 1:7.6+7ubuntu7
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.6.0-1ubuntu13
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:6.14.99~git20110811.g93fc084-0ubuntu1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.15.901-1ubuntu2
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:0.0.16+git20110411+8378443-1