I've submitted a patch to improve Firebird support. It runs best against a Firebird 2.0 database since rails uses certain queries with COLUMN = NULL in the where clause that won't work in Firebird 1.5
http://dev.rubyonrails.org/ticket/10287
If anyone here uses Firebird it would be great to try it out/review it and put some comments on it. You'll want to make sure to install the latest FireRuby driver from ruby forge.
Thanks, Scott Knight