Read/Write rules to prevent a Firebase entry-point from being mistakenly (or maliciously) overwritten:

gistfile1.js

{
  "rules": {
    ".read": false,
    "{{your-data-endpoint-root}}": {  // ie: blog
      ".write": false,  // prevents /blog from being overwritten
      "{{child-endpoint}}": {  // ie: entries
        ".write": false,  // prevents /blog/entries from being overwritten
        "$other": { // allows for writes to /blog/entries/{{key}}
         ".write": true 
        }
      }
    }
  }
}