Hi Andrew,
In theory, you could copy the data dlls and the Setup folder from the Firebird package for Windows and paste it into the pgsql package for Mono.
However, I will say that I still don't recommend Mono for important production sites. Currently Mono 2.6.1 is majorly broken as far as trying to use mojoPortal. With every Mono release it always seems like 2 steps forward and 1 step back, things get fixed and other things break. It has been that way for as long as I have followed Mono.
Currently I'm being encouraged by Novell to make a mojoPortal Linux appliance. I plan to give it a try after the next Mono release, but my fear is it will just be a support nightmare. Mono will have to stabilize before I would recommend anyone using the appliance for production sites, so I'm not even sure I should make one, but will probably give it a try and see how it goes.
Best,
Joe