@ybbond, I use these Terminal commands to change the Cmd-Q shortcuts to Cmd-Ctrl-Q:
defaults write org.mozilla.firefox NSUserKeyEquivalents -dict-add "Quit Firefox" "@^Q"
defaults write com.apple.Safari NSUserKeyEquivalents -dict-add "Quit Safari" "@^Q"
defaults write com.apple.finder NSUserKeyEquivalents -dict-add "Quit Finder" "@^Q"
then
killall cfprefsd
to quit/restart the cfprefsd
process which caches the preferences.