what is the best broweser for a mid 2007 2.4g ima

I just bought a used imac mid 2007 for my son. I got it to help with school and of course a couple of games for him to play. The browser installed is to old to download most apps and will not run most web pages. Any help would be greatly appreciated. Even if that advise tells me I made a mistake. Here are the specs.

2007 24in 2.4g 2 duo

4 GB 667 mhz ddr2 sdram

Thanks Josh