The possessive can go before an indefinite noun, but it must come after a definite noun. "vårt glass" (possessive adjective "our glass") or "glasset vårt" (possessive pronoun, kind of like "the glass of ours" except that in Norwegian this has more the meaning of "the glass which happens to be ours" The emphasis is less on the possession and this is the more common form.) http://grammatikk.com/pdf/Possessiv.pdf
Our glass? You have to share one? Then someone tries taking it, apparently?