In order for some of the upcoming filter enhancements to work, we had to fork rules.dat to rules1.dat. If you are going to use trunk builds going forward, your filter rules will be stored in rules1.dat. This is important if you change your filter rules by hand. rules.dat will also exist just in case you go back to using older versions. So changes made using one build may not be reflected in other.
http://bugzilla.mozilla.org/show_bug.cgi?id=168553 Navin
