xorg 100%CPU when I watch video on youtube

Binary package hint: xorg

When I watch video on youtube, xorg use 100% CPU and video lagging. Firefox is graying (not respond).

ProblemType: Bug
Architecture: i386
CheckboxSubmission: 6b8c1d5201f8c494caaa9536e2a5a343
CheckboxSystem: c422d78df84dd74685a7d007db671e12
Date: Fri Sep 25 11:56:24 2009
DistroRelease: Ubuntu 9.10
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
MachineType: ASUSTeK Computer INC. A7N8X-E
Package: xorg 1:7.4+3ubuntu5
ProcCmdLine: root=UUID=6ed258a1-616e-4ff9-ad44-5bcfa3c1ca4d ro quiet splash vga=769
ProcEnviron:
 LANG=pl_PL.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 2.6.31-10.35-generic
RelatedPackageVersions:
 xserver-xorg 1:7.4+3ubuntu5
 libgl1-mesa-glx 7.6.0~git20090817.7c422387-0ubuntu5
 libdrm2 2.4.13-1ubuntu1
 xserver-xorg-video-intel 2:2.8.1-1ubuntu1
 xserver-xorg-video-ati 1:6.12.99+git20090825.fc74e119-0ubuntu2
SourcePackage: xorg
Uname: Linux 2.6.31-10-generic i686
dmi.bios.date: 02/04/2004
dmi.bios.vendor: Phoenix Technologies, LTD
dmi.bios.version: ASUS A7N8X-E Deluxe ACPI BIOS Rev 1009
dmi.board.name: A7N8X-E
dmi.board.vendor: ASUSTeK Computer INC.
dmi.board.version: REV 2.xx
dmi.chassis.asset.tag: Asset-1234567890
dmi.chassis.type: 3
dmi.chassis.vendor: Chassis Manufactture
dmi.chassis.version: Chassis Version
dmi.modalias: dmi:bvnPhoenixTechnologies,LTD:bvrASUSA7N8X-EDeluxeACPIBIOSRev1009:bd02/04/2004:svnASUSTeKComputerINC.:pnA7N8X-E:pvrREV2.xx:rvnASUSTeKComputerINC.:rnA7N8X-E:rvrREV2.xx:cvnChassisManufactture:ct3:cvrChassisVersion:
dmi.product.name: A7N8X-E
dmi.product.version: REV 2.xx
dmi.sys.vendor: ASUSTeK Computer INC.
fglrx: Not loaded
system:
 distro: Ubuntu
 architecture: i686kernel: 2.6.31-10-generic

[lspci]
03:00.0 VGA compatible controller [0300]: ATI Technologies Inc RV350 AP [Radeon 9600] [1002:4150]
     Subsystem: PC Partner Limited Device [174b:7c29]