This worked. I use Root Explorer and I hadn't tried the long press. When you tap it, it offers a small set of apps to open it with including, in my case, Firefox and Chrome, but not Fulguris. But when I long press and do open with, I get a very rich set of choices, including all apps. I was able to open with Fulguris and then make a bookmark to the file, which works great. 👌
Not on my Pro1. Shows up as Fulguris, not Lightning. But thanks for the tip! 🙂