Tim Anderson does a side-by-side comparison of Silverlight and Flash for calculating prime numbers. He has written the program in both platforms. I thought I'd add a Javascript version into the mix too. The results were as follows:

Calculating 1,000,000 primes

• Silverlight: 0.42 secs
• Flash: 1.22 secs
• Minefield 3.1 Javascript: 4.75 secs
• Safari Javascript: 5.75 secs
• Firefox 2 Javascript: 7.08 secs

I actually thought that Minefield (Firefox 3.1 with TraceMonkey Jit) would be up there with Flash and Silverlight. I guess that the JS Jit works on hot paths and therefore couldn't find much to do?

UPDATE

@Shi posted another version in the comments with much improved times:

• Minefield 3.1 Javascript: 1.88 secs
• Safari Javascript: 4.99 secs

That's more like it!