I'm running a Geb test using WebDriver 2.41.0 and Firefox 29. The page source includes:
<input type="number" data-type="range" data-highlight="true" max="110" min="0" value="0" id="CarArmorSingleFront" name="CarArmorSingleFront" class="ui-input-text ui-body-c ui-corner-all ui-shadow-inset ui-slider-input ui-focus">
This appears as a text field with tiny up and down arrows, which seems relatively new to me (as opposed to a plain text field without the up and down arrows).
Anyway, the test tries to write a blank string to the field, which works, followed by trying to write the value "16" to the field, which erroneously does nothing (the cursor is still in the field but the field is left blank).
It worked fine (e.g. wrote "16" to the field) with Firefox 28.
Thanks,
Aaron