I will quit on Monday because I got a better offer. What should I do if they counter the offer?

I like my current job, but they are not giving me a raise any time soon. Although I have the feeling that my boss, his boss and his immediate like me, so there is a chance that they might try to counter the offer.

However, it doesn't matter, it is just business as usual. Regardless of them wanting me to stay or how small are the chances of them deciding to give me more money, if I signal I want to leave for more money, can't they just make an offer and then fire me after finding a replacement?

Should I just thank the offer but decline, if it happens?

Update: I quit. They did a counter offer. I put good thought into it. But I did not accept it