If you have PR 1.2 installed on your N900 than microB comes with geolocation. No need to install an add-on. Likewise with Fennec (comes built-into the browser).

I'm assuming the only thing it does is allow you to check in to a nearby location (based off your GPS location) or specify a name for your location since that's what I've seen when I tested it . I'm assuming it works after that (again haven't tried since I have no interest in letting people know where I am) since it had already figured out the nearby places. I'll try sometime this week when I have some free time. Probably on one of the days where I'm going to class.