PM> Install-Package FirebirdSql.Data.FirebirdClient
PM> Install-Package EntityFramework.Firebird

<configuration>
    ...
    <entityFramework>
        <defaultConnectionFactory type="FirebirdSql.Data.EntityFramework6.FbConnectionFactory, EntityFramework.Firebird" />
        <providers>
            <provider invariantName="FirebirdSql.Data.FirebirdClient" type="FirebirdSql.Data.EntityFramework6.FbProviderServices, EntityFramework.Firebird" />
        </providers>
    </entityFramework>
    ...
  </configuration>

<configuration>
  ...
  <connectionStrings>
    <add name="DefaultConnection" connectionString="User=usuario;Password=senha;Database=C:/caminho/do/arquivo.fdb;DataSource=localhost;Port=3050;Dialect=3;Charset=NONE;Role=;Connection lifetime=15;Pooling=true;MinPoolSize=0;MaxPoolSize=50;Packet size=8192;ServerType=0;" providerName="FirebirdSql.Data.FirebirdClient" />
  </connectionStrings>
  ...
</configuration>