Remove references to private script _downloadURL properties.
Remove references to private script _downloadURL properties.

Refs #1800

Ventero/greasemonkey,Martii/greasemonkey,Martii/greasemonkey,HasClass0/greasemonkey,Ventero/greasemonkey,the8472/greasemonkey,the8472/greasemonkey,HasClass0/greasemonkey