You should not touch
~/.fgfs/Aircraft/org.flightgear.fgaddon/Aircraft/ (even if all other aircraft are there, that directory is managed by FlightGear).
Instead:
- unzip the .zip file you downloaded and, if needed, rename the directories by removing -master as explained in my previous post;
- create a folder where you will store the downloaded aircraft (e.g. /home/jono/FGAircraft, but you can use any path you wish);
- move the directories you extracted from the .zip files into /home/jono/FGAircraft;
- start the FlightGear Launcher, open the "Add-ons" tab, in the "Additional aircraft locations" section click "+" and select "/home/jono/FGAircraft" from the window that appears (note: you will need to do this only once).
By the way, with the newest FlightGear version you do not need to download official aircraft manually - just open the Aircraft tab, make sure the "Only show installed aircraft" checkbox is unchecked, choose the 777-200 and click on Run - the aircraft will be automatically downloaded from the official FlightGear hangar. (If, on the contrary, you are trying to run a 777-200 from a third-party hangar, you will need to follow the instructions I gave above).