How do I stop the page refresh on pressing "enter" in a form's text field?
You need JS/JQuery assistance in this regard.

var stopSubmission = false;
jQuery('#q').keydown(function(e){
   if(e.keyCode == 13){
       stopSubmission = true;
   }else{
       stopSubmission = false;
   }
});

jQuery('form[action="/help/search"]').submit(function(){
    if(stopSubmission){
        return false;
    }
});