Should I get a lifetime alignment?

No such thing as lifetime alignment unless they mean they'll align for free anytime you feel you need one. Only problem I see with that is when you go in they'll be trying to sell you steering or suspension parts, so be care full. Also should be 4 wheel alignment. Sorry don't trust Firestone. If front end parts OK and can be aligned properly shoulsn't need more than once a year, unless replacing tires.