To dream of a glass jar represents something about yourself or your life that you want to notice whenever you want. An issue that you feel you should be able to bring up whenever you want or feel good about whenever you need to. It may also reflect resources or opportunities that you like having access to at all times. Having as much of an experience or feeling as you want.
Example: A woman dreamed of an ugly lizard creature inside a jar. In waking life she liked talking about how horrible her cancer experience was. The creature in the jar represented the horrible experience of her cancer that she valued herself for confronting and liked being able to discuss as much as she wanted.