use single combined welcome message
fix jshint errors
don't use array.from due to support for older versions

Navigator.mozMobileConnections started to exist with ffos 1.3 [1], which is based on gecko 28 [2], while array.from started to exist with gecko 32 [3]

[1] https://developer.mozilla.org/en-US/docs/Web/API/Navigator.mozMobileConnections
[2] https://developer.mozilla.org/en-US/Firefox_OS/Releases/1.3
[3] https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/from#Browser_compatibility