Proper DOM help - HELP: Strict JavaScript Syntax Checker Verifier

Two quick questions:

1. I really love Mozilla Firefox's javascript.options.strict mode (type about:config in addressbar). However it still doesn't pick up on certain things such as making it compulsory to have semi-colon as a statement terminator. I have hundreds of organically grown JavaScript files that are millions lines long. They are not written by me but by former employees and I've been handed the job of debugging & fixing their code. Does anyone know of a good Very strict JavaScript syntax verifier checker? What is the best JavaScript IDE out there?

2. What happens if I keep on writing:

var control = new Control();
var control = new Control();
var control = new Control();

500 times? Will this cause a memory leak? Or will the previous object be deleted since the reference is lost? Or is it handled differently in IE & FF?