"The WebKit project initially landed the SquirrelFish Extreme jit on September 18, 2008; it's pretty clear that this was in the works before Chrome's existence was announced."
In fact, the Apple WebKit folks have said that they began the Squirrelfish Extreme project the day after Tracemonkey was announced. It was quite an engineering accomplishment to have an initial stab at a JIT in a month and have it shipped to users in a few more, especially considering it took Mozilla about a year (Summer '08 - June '08) to ship theirs. And everyone knew about Tamarin's development over the previous couple years - so it ended up being a really amazing coincidence that all three JITs were announced within a one month period.
In fact, the Apple WebKit folks have said that they began the Squirrelfish Extreme project the day after Tracemonkey was announced. It was quite an engineering accomplishment to have an initial stab at a JIT in a month and have it shipped to users in a few more, especially considering it took Mozilla about a year (Summer '08 - June '08) to ship theirs. And everyone knew about Tamarin's development over the previous couple years - so it ended up being a really amazing coincidence that all three JITs were announced within a one month period.