If you're using the (default) embedded version Firebird, I suppose it's going to lock the database and cause a "freak out." For those who want to open another instance of the program for a different database, a more graceful behaviour would be to present a File Open dialog. A workaround would be to use the -portable switch for the second instance. This will force the program to use a different configuration file (in the application directory) which can point to a different database.
I'm not sure, but I imagine the bug reporter is just using mailto. If you choose to use webmail, it's up to you to configure your OS and browser so mailto invokes your chosen webmail application.