Developers must manage manual linking 1. Developers must manage manual linking To avoid these issues, developers should implement linking logic (`linkWithCredential`) that allows a user to connect multiple providers to a single account. This requires a clear interface and client-side checks. 2. Why this behavior is intentional Firebase prioritizes security over convenience. Automatically merging accounts could expose one user's data to another if the email address is shared or misconfigured. By keeping accounts separate, Firebase prevents critical identity errors. 3. Tips for users If you use multiple login methods (Facebook, Google, Email), try to maintain consistency. If you already have an account, log in with the initial method and link the other providers from the site settings, if this option is available.