Hi
I make a test using your sample JSON data, and I get table as shown in the following screenshot, does it return your expected result?
If yes, please add the following codes in your Advanced Editor.
let Source = Json.Document(Web.Contents("url to firebase database")), #"Converted to Table" = Record.ToTable(Source), #"Expanded Value" = Table.ExpandRecordColumn(#"Converted to Table", "Value", {"name", "age", "maritalStatus"}, {"Value.name", "Value.age", "Value.maritalStatus"}) in #"Expanded Value"
Thanks,
Lydia Zhang