How in God's name do you install HYBY lamp?

I bought the HYBY lamp and wired it up no sweat...trying to put that freaking glass dome on has driven me mad.

According to the instructions you are supposed to hook 2 of the clear plastic arms on to the rim of the dome and then apparently bend the 3rd arm until it snaps onto the dome rim...every time the arms pop off as I try to get the last arm engaged...Has anyone else come across this?