I've kept them in the past and am just in the process of setting up a new DIY jellyfish tank. The first thing you should do is find out what type of jellyfish you're dealing with. Some are more suitable to aquarium life than others. Most have a very mild sting or none at all (to us anyway). Some are quite literally... deadly. However, the chance of finding 'deadly' jellyfish around Boston is slim. Chances are highly likely that they are moon jellyfish (Aurelia aurita) which are relatively harmless to people (who do not have allergies to their stings). All a person might feel after being stung by Aurelia aurita would be a mild irritation if any at all. The only time I've felt anything while handling Aurelia aurita is if the tentacles come in contact with an open cut or sore (not fun). And, they are the most commonly kept (and bred) jellyfish in aquariums. I've kept them and I know of a number of people who have had them in aquariums.
They are not that all that difficult to keep in captivity. Provided that you have a properly set-up aquarium (Google "kreisel aquarium jellyfish" & you'll find plenty of info) and are committed to doing a few minutes of work EVERYDAY. And yes, any jellyfish that you find around Boston will require a chiller. There are no short-cuts there. That's why I spend a good deal of effort hunting around suppliers that are in the tropics and shipping them up here to Canada.
Widmer's book is an excellent resource for anyone thinking of starting to keep jellyfish.
I made a quick video the other day of a water flow test I did when I got confirmation that my jellyfish were being shipped. The test is done with Kleenex as soaked Kleenex is moved around by the flow in the tank in a very similar manner as a jellyfish.
I'm going to make another video of how the tank is put together and how it works once I've got the jellyfish in it. And, another one of the jellyfish.\\