Is Firefox 4.0 faster than Chrome 10 ?
No, Chrome 12 is the fastest, next comes Firefox 5. It's better if you use/upgrade Chrome to 12th version.
The versions you have mentioned are outdated and not used anymore. Nowadays, Firefox reached version 24.0.1 and Chrome 29.0.1547.76. Both browsers are optimized and are very fast regarding the way they work.