Comment by uzegonemad

I override this at a system level for some apps (e.g. Firefox, VS Code) by taking the following steps:

  1. Open System Prefs and go to Keyboard > Shortcuts
  2. Select "App Shortcuts", then press the + Button
  3. Choose "Firefox" (or other relevant app) from the dropdown
  4. Type *exactly* the name of the menu option that has the CMD + Q shortcut next to it, in this case "Quit Firefox"
  5. Focus on the Keyboard Shortuct input and choose whatever new key combination you want to be used for quitting the app. I usually use CTRL + CMD + SHIFT + Q
  6. Press the Add button

This video is older but also shows the general process: https://www.youtube.com/watch?v=YWbEBipLxKA