Using ODBC Connection to Access Firebird Database
You should be able to create a Linked Server to almost any ODBC data source.

I would suggest trying the Microsoft OLE DB Provider for ODBC Drivers.

While you need to enter something in the Product Name field, I believe you can enter anything, such as "Firebird".

For Data Source, enter the name of the ODBC System DSN you've previously created.

You'll need to confirm the other options for "Security" and "Server Options", and test to see if it works.