It would be nice to see more information about optimizing for IE and Firefox's JS engines, but to be fair, V8 accounts for a large percent of browser JS and all of Node.js as well.
Node.js is the answer, here. Most stuff you do on the client (outside webgl and game calculations) shouldn't be impacted heavily by these kinds of optimization snafus. But if you're trying to get your server to be as performant as possible, these can really kill you if you snafu naïvely.
