I have used custom function for validating my date text. 

 colModel: [ {name: 'startDate',index: 'startDate',width: 50,align: 'center',sortable:false,edittype:'text',editrules:{custom:true,custom_func: checkDate}],

function checkDate(value,valueRef)

{

if(value=="")

{alert(invalidDateValue);

return [false,''+invalidDateValue+'']; 

} 

}

On Enter press this validation message being displayed for short span of time and request is sent to server although I am returning false.

But this is not working in Mozilla 23.0.

the same code is working fine in IE//Chrome.