Only allow proper values for run-at, otherwise default.
Only allow proper values for run-at, otherwise default.

Refs: #1103

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