Why did the latest version take a step backwards and remove the QUIT option from the toolbox?
Do you mean the exit button to quit the Firefox browser?
I am still seeing the button by going to the [Firefox] menu on the top left corner, running on version 19.
Please let us know if this is what you mean.
rjbd this is a Firefox for Android question.
You can easily quit Firefox just like any other app on Android 4+.