You will need to install operator. Operator has support for poshZones. Thanks to Mike for tweaking operator to let poshZones work as a pluggable format. I had initially called it a flexiFormat but then poshZone better conveys that it basically works off plain old semantic HTML. Once you install the XPI from the latest build into FireFox, you can plug-in support for poshZone by registering the poshZone script and some sample actions with operator.
Note: I am not trying to subvert formal microformat efforts. I just think you need more flexible classification than the likes of hReview. From a user's point of view, it matters hugely whether a review refers to a book or a restaurant or a movie. I can't add a restaurant to my movie rental queue. hReview doesn't seem to have a way to indicate this as yet. For things like events, we could very well continue to use hCalendar and still have user scripts that let us do flight lookups etc.
PoshZones get you up and running without waiting for a formal microformats specification. At the same time, this could serve as useful real world input for ongoing formal spec efforts.