I think that these vaseline pigs were made by Thomas Webb & Sons for an exposition in the early 1900s...the company actually had a mini glass-works set up on site to demonstrate glass-making skills to the public.
The pigs proved to be a very popular souvenir.
I don't have access to my reference books at the moment, so I can't provide exact details...but the book "Art, Feat & Mystery-the story of Thomas Webb & Sons,Glassmakers" illustrates a similar example to yours, along with it's original packaging.
What a nice find to have in a charity shop!
