Fix Bug 941392 - Ugly forms in "subscribe" popup at https://www.mozilla.org/firefox/os/, on GNOME 3

Remove style for the select element.
Merge pull request #1783 from kyoshino/bug-941392-select-height

Fix Bug 941392 - Ugly forms in "subscribe" popup at https://www.mozilla.org/firefox/os/, on GNOME 3