Thanks for all the replys ! I've found a way to upgrade to 1.6.0 ok it's not 1.6.3 as I wanted but better than nothing.
What I've done:
1.uninstalled ff6 with all data and cache.
2.downloaded apkpure and ff6 6.6.2 in the xapk version with the obb file included.
3. Before first start of ff6...