If it is just turning brown around the edges then it is slowly dying. If you see little roots on the back of the leaf that is baby ferns. Don't fret if you see some browning, plants won't last forever, just encourage new growth by giving it light and nutrients.
One of my java ferns would grow babies on the entire back side of the leaf, and the other grew them on the ends of the leaves. After removing the spores off the end of the leaf, it would usually look brown like how it is in your second picture
Btw I have some flourish liquid fertilizer, I hardly used any of it, probably less than 5% off it. It was like $9 at petsmart, If you're interested I can see how much it would cost and I'll give it to you if you can pay shipping :)
Good luck with the plant I dont know anything about Java Ferns but I did just order one so would like to know how yours is doing along the way. Are you going to put it in your tank ?
Theyre little brown spots on the leaves, and baby java ferns grow from them. Once they're big enough and have roots and a leaf or two, they will fall off or you can remove them. Mine grew a ton after adding the fertilizer.
Yeah I would give it some light while its in QT and maybe even set it outside to get some sunlight, thats what I did with my Anacharis and Hornwort and it seemed to help they are doing great in the tank now. Also when you do a water change save some water and use that to put the Fern in so it can get used to your water, I did that too with my plants.
Thanks Teeney thats very cool I would have seen that and freaked out thinking it was snails or bugs...lol