dxdy at gsmarena figured out a way to download firmwares from Navifirm+ using the old cache.
Download the cache from here:https://mega.co.nz/#!Y0RjTYDa!cs_O_1_gJU3inSiaE20fbX42BH1IvHZIrLKsRmmb3wk
Paste the cache into navifirm's cache folder.
Enjoy downloading firmwares again!