Hey there! :)
Chrome extensions are more or less miniature, self enclosed web apps; seeing as that tends to be my expertise, I'd be happy to help. That said, I am curious what sort of extension you're looking to create? Your job description is a bit brief, after all. Either way, I'd love to discuss your project with you.
As for the standard "about me" formalities, I've been using JavaScript both professionally and as a hobby most of my life, and while I've only recently joined Freelancer.com, I've been freelancing as a JavaScript expert for quite some time now. By all means, feel free to check my profile for a few testimonials from past clients, as well as to get to know a bit more about me.
With that out of the way, I'd love to hear from you as soon as possible. Toss me a reply so we can get started right away! I look forward to working with you. :)