MAC addresses in JavaScript

The quick and simple answer is No.

Javascript is quite a high level language and does not have access to this sort of information.

I concur with all the previous answers that it would be a privacy/security vulnerability if you would be able to do this directly from Javascript. There are two things I can think of:

• Using Java (with a signed applet)
• Using signed Javascript, which in FF (and Mozilla in general) gets higher privileges than normal JS (but it is fairly complicated to set up)