I use the following code in my app and it is working in anything but Firefox 3.6.11. I couldn't type anything including numbers in the field.

NumberField amount=
new NumberField();
field.setName("amount");
field.setFieldLabel("Amount");
field.setFormat(NumberFormat.getDecimalFormat()); // The same result for any other format
field.setAllowDecimals(true);

field.setAllowBlank(false);

Did I do something wrong?