redircted en-AU locale to en-US

Hi,
As there is no en-AU localisation for Firefox, attempting to download any version of Firefox without specifying the localisation ends in failure.
I propose that en-AU redirects to en-US (the nearest equivalent locale).
I'm pretty new to doing pull requests so pre-apologies if this is the wrong way to do it or something.
Also incidentally when it can't find a locale it doesn't fail very gracefully. 
It attempts to create a profile and believes it succeeds. Hitting 'y' to install firebug then causes it to hang.
Cheers,
Callum.