Are any JavaScript engines tail call (TCO) optimized?

The ECMAScript 4 specification was originally going to add support for TCO, but it was dropped:

No more tail calls in JavaScript?

As far as I know, no widely-available implementations of JavaScript currently do automatic TCO. This may be of use to you, though:

Tail Call Optimization

Essentially, using the accumulator pattern accomplish the same effect.

No joy for the moment, but thankfully proper tail calls are slated for Harmony (ECMAScript version 6) http://wiki.ecmascript.org/doku.php?id=harmony:proper_tail_calls

Pretty much every browser you encounter will barf on "too much recursion". Here's an entry in the V8 bug tracker that will probably be interesting reading.

If it's simple self-recursion, it's probably worth the effort to use explicit iteration rather than hoping for tail-call elimination.