HD videos on youtube tend to lag in firefox 3.5.1 for Ubuntu 9.04

[froggyboy604]

My computer specs are

CPU 1.6 GHZ P4
RAM: 512 MB of DDR SDRAM 266MHz
Video Card: Nvidia Quadro FX 500 128MB
Hard drive: 200GB 7200RPM

I'm using the latest version of Ubuntu 9.04 .

I think it might be a driver problem with the videocard, or the videocard being too slow, overheating.


Any ideas on how to fix this?