I have the same issue. While upgrading from version 2.2.0 to version 2.2.4, I've noticed that LiveGrid vertical scroll stopped working in Firefox.
We have a premium support subscription. When can we expect the version 2.2.5 with LiveGrid fixed?
The fix is already in SVN. You can build your custom GXT from there. Depending on your support subscription we also custom builds. You should open a real support ticket for this under http://support.sencha.com