Chord Progressions

Depends on where you got that progression from and for what purpose you want to save it.

If it's already in Synfire, drag it to a library for re-use (left side bar under the book icon). That will save it with the library. From there you can drag it to other arrangements (or anywhere else for that matter).

Maybe I didn't understand your question right, though.

If you have only a single progression to save, you can copy it to the progression editor and save it from there. Open the progression editor (File >> New >> Progression), copy your progression into the progression editor (simply drag the "Harmony" parameter of your arrangement to the progression editor) and then save the progression with the Save command. It will save as a .cogpro file. Re-using of the progression then proceeds with the reversed steps.

If you have multiple progressions to save, you should use a library, as Andre mentioned.