Add-ons for Australis contest promotion (bug 979731)

https://bugzilla.mozilla.org/show_bug.cgi?id=979731

**Screenshots:**
![discoverypromo](https://f.cloud.github.com/assets/187006/2336957/c6b9e420-a496-11e3-9785-65401bd37486.png)
![mainpromo](https://f.cloud.github.com/assets/187006/2336956/c6b96284-a496-11e3-9ea3-528f97b31916.png)