HTML5 input type number not working in firefox

Alternately, you can use a textfield with a pattern="" attribute. Although it doesn't have the up and down buttons, it does validate for having the correct values:

<input type="text"
       name="quantity"
       pattern="[1-9]"
       value="1"
       required
       title="Qty"
       class="input-text qty text"
/>

You can alter the pattern to your quantity wishes, it is now set for a value ranging from 1 to 9. Also you can add up/down buttons with JS/jQuery that have hotkeys bound to them for a more number-field-like feel.

It is not supported in firefox or internet explorer, except for version 11 which has partial support. See this comparison matrix.

You can use the number polyfill shim to get support for unsupported browsers.