Those are considered "helper" bags for heavy loads, the max load and pressure amount would be determined by the model # most likely. The tough part is knowing what kit you have installed but if you can get some clear pictures of all the components including any part #'s, that may help determine what you have.
The one thing to keep in mind is most of these setups are designed to run with some air in them at all times, or the bags can become damaged. I forget how much is minimum unloaded pressure spec - but at least 10-20 psi is probably a good starting place. Some searching on Firestone's site could get you some useful info. Here are some very general tips -
https://www.firestoneip.com/ride-rite/technical-tips/
BTW if they're just on there because they came with the truck, and you don't really need them, you might do well to carefully remove the kit whole and offer it for sale. Otherwise, you're gonna constantly be tending to whether they have the minimum amount of air to prevent damage to the bags, and that can be a chore when you have the manual (no on-board compressor w/gauge) kit.
Richard