I love that "what he said" gif, I'm going to steal that
Fireworks aren't actually that hard, it's all at infinity, so pre-focus manually at ∞ and leave it on manual. You can use a fairly large aperture, to capture lots of light, just choose an ISO vs. shutter speed that suits the look you're after. Use IS.
Restaurants are a challenge, you can't do it well, you have to fake it somehow. I'm sure a professional would insist on using a flash - somehow I have the feeling that if a pro insists they need to use flash, people accept it, which makes the whole situation rather self-sustaining! If a proper flash unit to bounce of walls/ceiling is unacceptable, try a pop-up flash diffuser (google gary fung).
If flash at all is a no-go, then you have to either frame your photos 'flat' - i.e. everything you want is at one distance, so you can use a wide aperture without losing stuff; or you have to whack up the ISO and accept a noisy photo. There are tools to reduce noise in post, or you can simply resize away the fuzz and make a thumbnail photo, or just tell people that the grainy look was what you were aiming for, to illustrate the restaurant setting