Firebase usually just accepts what you send it, so if you add quotes it will include them in the field
e.g.
store: Hello World firebase will store and return Hello World
store: 12345 firebase will store and return 12345 (AI2 will interpret anything hat looks like a number as a number on return)
store: "Hello World" firebase will store and return "Hello World"
store: /my/file/path/image.jpg firebase will store and return /my/file/path/image.jpg
store: "/my/file/path/image.jpg" firebase will store and return "/my/file/path/image.jpg"
That has been my experience...