1. No. A single Google Cloud project can only be “upgraded to Firebase” once, meaning you cannot attach multiple Firebase projects to the same Cloud project.

2. Because each Firebase project maps to exactly one Google Cloud project Each Firebase project has its own:

• Authentication users
• App tokens
• API keys
• App identifiers

Since each Firebase project equal to each Cloud project, none of these can be shared between Firebase projects.

3. Recommened way is to create multiple apps for each environment for a single firebase project.