FYI: Probably the two threads No internet at all and No data connection after update to 1.4,2 and rooting were related to this thread.
I think that my unsolvable problems with internet connection were triggered by changing platform.xml in a wrong way. After I couldn’t find a solution to bring back the internet connection I sadly reflashed my phone with Open OS 16.06.
Today I have changed again platform.xml in regard to SD Card no writing permission in FP2 (but I used Ghost Explorer instead of Amaze) and I mentioned that after saving platform.xml the read permissions for group and others were missing.
So I gave back read permissions to all on platform.xml before remounting /system with RO option and rebooting and the phone is still running 
But I don’t know for sure if this approach is saving the phone from bricking.
Update: No, it doesn’t. Saver approach see here: SD Card no writing permission in FP2