Is there way to downgrade all packages back to stable? I've installed some packages (irssi and shorewall) from testing and then I found backports. Now I'd like to downgrade all back to stable and start using irssi and shorewall from backports so I wouldn't have to keep all those libraries and tools from testing.

Well, if there's a problem, it will be with the libraries. Though I am not sure how many packages are involved, I'm also not sure if simply removing the packages would solve your problem.

I'd start with this approach, though, take notes, and see what happens:

apt-get remove irssi shorewall

(and see if anything else gets removed with them. If the actual package names are different, use the appropriate package names).

Then install, specifying stable:

apt-get install irssi/stable shorewall/stable

Hopefully, if there are any backward dependencies, best case, they will take care of themselves. Worst case, at least the apt-get program will complain about what needs to change. In the worst case scenario, you may end up having to manually apt-get remove additional libraries, then apt-get install them again, specifying /stable as with the main packages. With a bit of luck, all will go smoothly, the packaging system will deduce what you need and do it right. The likely scenario is that you may need to manually remove a few things, but you might get some packages to "come along for the ride".

--oops--