My son made a snow dome from a jar in pre school, he still has it now 4yrs on he loves it but I don't exactly know how it was made.
It looks like the xmas tree (decoration) was made out of play dough and somehow stuck to the lid ( I don't know with what) it was probably then screwed on the jar that was full of water and had glitter, then tightly sealed then taped with electrical tape.
This is only how I think it was done, I'm not totally sure.
This site may help more than I can
http://www.homeschoolzone.com/craft/glitterdome.htm