When I run npm run start I get the below error regarding firebase.
Tech: Angular version 9, Firebase, Firestore, Geofirestore Angular CLI.
I Have to been facing same error.
I just installed angular cli 8th version. My previous angular cli was 10.
step 1> npm cache clean --force
step 2> npm uninstall -g @angular/cli
step 3> npm cache clean --force
step 4> npm install -g @angular/cli@8.1.0
step 5> ng new project_name
step 6> ng add @angular/fire firebase
Hope so every thing works well.