Firebird V1.0 and interbase Open source 6.0.1.6

I known Firebird and interbase is compatiable but i want to know is

1. Is need to use IB to backup GDB and restore it in Firebird .

2. Sometimes ago , i decide to go back IB , can i just copy gdb to
original IB server,or Backup in Firebird and Restore in IB . or it's
impossible (Assume no Firebird feature add in the GDB)

3. If i use Firebird 16K pagesize , can i backup the GDB and restore
in IB Use 8K pagesize .

Thanks in advance.