> How would one normally deal with this problem? Presumably one must always use globally unique keys, but can these be generated in firebird?

Three usual solutions:

1) composite Primary Key, which include unique database ID;
2) Ranges, as mentioned by Helen;
3) UUIDs, also already mentioned.

Choose one, which is most suitable for you. Note, that not all
applications can work with binary UUIDs.

SY, SD.