I'd imagine by the time your program's security is critically reliant on ASLR and process-level sandboxing, you're already in deep trouble, since any given minor update may turn existing holes into viable exploits. It will only slow down the rate of attacks at best.

The lesson I'd take here is "don't embed a web browser to run untrusted code unless you can keep it up to date 24/7". Hence the popularity of Lua interfaces for mods. Or even the alternative JS engines built for such purposes.