The official firebase website has a link to download the latest version of their SDK for Unity. The page is here and links to the following URL.
Download Latest Unity SDK
https://firebase.google.com/download/unity
Older versions
To download older versions, you can use a direct link like below.
Download arbitrary Unity SDK
https://dl.google.com/firebase/sdk/unity/firebase_unity_sdk_X.YY.Z.zip
For…