onclientclick in firefox not working?

<asp:ImageButton ID="removeButton" runat="server"  OnClick="removeStudentInformation" OnClientClick="return checkBoxselectedornot()" ImageUrl="~/image/remove-selected-button.png" />

function checkBoxselectedornot() {

       
        var valid = false;
        var gridview = document.getElementById("studentInformationGrid");

        for (var i = 0; i < gridview.all.length; i++) {
            var node = gridview.all[i];
            if (node != null && node.type == "checkbox" && node.checked) {
                valid = true;
                break;
            }
        }
        if (!valid) {
            alert("Invalid. Please select a student to continue.");
        }

        return valid;


}