Pretty much as the title says really!
If you are building a webapp for Firefox OS it used to be that to install the manifest file you would call
navigator.mozApps.installPackage('path/to/manifest') but this has been changed to just be
This tripped me up recently as I was following an old guide and I couldn't work out why something that I was positive worked before no longer worked!
I think this syntax is a lot cleaner.