That is actually somewhat useful. I don’t know if that use-case is worth it to me, personally, to have a potentially insecure device on my home network, but I suppose you could give it its own network and write decent firewall rules to protect your other gear.
I’m dumb, and had to reread what you wrote. I thought you meant tabs this whole time (doh). I haven’t even used an iPad before, so I didn’t know that feature existed. I don’t believe I’ve ever seen multiple windows of Firefox on Android (but you can have multiple apps open side-by-side).
I think it is unlikely Mozilla would support that feature, given the lack of resources and demand; iPad’s are niche.