DHT11 data in Arduino UNO to Firebase through ESP8266
First of all, FirebaseArduino.h library is for ESP8266 itself and not for Arduino UNO.
The code you have written will not work as you are giving instructions like Firebase.setFloat("temp",t); to UNO. It will not compile.
What you should do is set ESP8266-01 as your primary board and let the UNO transmit the data by software serial.
ESP8266-01 will capture that data and transmit it over the Internet.
YOU CAN'T USE FirebaseArduino.h FOR ARDUINO UNO! It is for the ESP8266.
All YouTube videos will show you how to code for NodeMCU esp8266-12E. Do that for ESP-01 and communicate with Arduino for data (converting data calculated to string will help to reduce problems). Get data in form of string from UNO and transmit it using ESP-01!

If you want I can share all video list that I found useful!