Bootrom 359.3

From The Apple Wiki

S5L8920 bootrom revision for the iPhone 3GS sold between June 2009 and September 2009.

This bootrom is vulnerable to the 0x24000 Segment Overflow and limera1n Exploit, which together provide a "pwned for life" untethered jailbreak. This also means that you can restore to any iOS version that the 3GS has had without SHSH blobs. Compiled in between 2.0 and 2.1