Incorrect sizing of submit button on firefox mobile

[johncrawley]

Steps to reproduce:

• install the Say, Pi Firefox Add-on on an Android device
• notice how the submit button inside the text field is slightly squashed horizontally

This issue is only visible in landscape mode and when the Say, Pi Add-on is installed.

[johncrawley]

Added changes to make buttons look better on mobile devices with smaller screens (720px width). Still need to verify on mobile devices with larger resolutions (1440px width).

[johncrawley]

Not reproducible on a Samsung A16 phone (1080 x 2340), or a Nokia C32 (720 x 1600).