Fix pageNumber input field in Firefox Nightly

With recent changes in Firefox, the pageNumber input field no longer looks right, see below.

* __This is how it *should* look:__
Screenshot taken in the latest Aurora (Mozilla/5.0 (Windows NT 6.1; WOW64; rv:27.0) Gecko/20100101 Firefox/27.0 ID:20131209004003 CSet: 0ff7a838c4be).
![aurora](https://f.cloud.github.com/assets/2692120/1708594/2d84e52a-6111-11e3-8623-2cfb5d25b95c.png)

* __This is how it looks now:__
Screenshot taken in the latest Holly, i.e. Firefox Nightly without Australis (Mozilla/5.0 (Windows NT 6.1; WOW64; rv:28.0) Gecko/20100101 Firefox/28.0 ID:20131209081648 CSet: 894b56f8bbf5).
![holly](https://f.cloud.github.com/assets/2692120/1708602/577027fa-6111-11e3-88f0-48404e81a983.png)

It appears that with the improvements of HTML5 input elements, `<input type="number>"` isn't what we want to use for the pageNumber field. This patch fixes the issues by changing it to a standard `<input>` element.