compiler error with ESP8266

Hi every one

I tried to use FirebaseDemo_ESP8266 and connect esp8266 wifi MOD to my PC but I got compile error

every time ... " Error compiling for board Generic ESP8266 Module" and also fatal error: ArduinoJson.h: No

such file or directory

I installed Generic ESP8266 and add its library with firebase library but the error still with me ..

by the way I selected Generic ESP8266 board .

please can any one help me?

I installed Generic ESP8266 and add its library with firebase library but

apparently not the ArduinoJson library. Why not?