Grid not rendering in firefox

I am working with EditableGrid to generate and manipulate column models dynamically. Everything has gone according to the plan, except for just one compatibility issue with Firefox (..yes not IE -_-). I understand this is some sort of Closure issue maybe? I cannot seem to work a way around this. This is where something goes wrong:

EditableGrid.prototype.initializeGrid = function () {
    with (this) {
        //apply cell validators and inforenderers in headers
        var regex = [];
        for (var count = 0; count < selectedColumnNames.length; ++count) {
            var columnObj = findSelectedColumnObject(selectedColumnNames[count]);

            //check if regex is provided
            if (!(columnObj[0].validationRegex == "")) {
                // add a cell validator
                var expression = new RegExp(columnObj[0].validationRegex);
                regex[columnObj[0].name] = new RegExp(columnObj[0].validationRegex);
                var valObj = GetValidatorObject(expression);
                addCellValidator(columnObj[0].name, valObj);
            }
        }

        function GetValidatorObject(regObj){
            var obj = {
                isValid: function (value) {
                    return value == "" || (regObj.test(value));
                }
            };
            return new CellValidator(obj);
        }
}

The exception it throws is:

ReferenceError: GetValidatorObject is not defined [var valObj = GetValidatorObject(expression);]

Any ideas?

Thanks to epascarello, the work around was simple, I moved the method of GetValidatorObject out of the scope of with (this). Now it works with FF. When I further digged into the matter, I found avoid using 'with' keyword in JS really interesting. This might clear grey areas.