You can upgrade/downgrade to any revision of Raspbians firmware using rpi-update. For example if you want to install revision 3.10.25+ you should execute this:
sudo rpi-update 2ef601a50b68eebeeb4dc3c6c525855961891be6
The long string represents the Git hash for the specific firmware revision. You can look for those hash in the rpi-update git repos commits list: https://github.com/Hexxeh/rpi-firmware/commits/master.
Look for the commits having “kernel: bump to 3.X.X” and click the boton on the right:
Now you can see the whole hash string in the url:
