Get the extension here. (You'll have to right-click -> Save Link to Disk... then execute.)
The thing that's finally got me off my arse and registered with SixApart's fancy blogging tool is Greg Reinacker's NewsGator. It's a fantastic tool, perfect for wasting less time loading blogs and more time reading them. It lacks, however, in the area of Mozilla integration.
I use Firefox as my primary browser (heh, what self-respecting wannabe geek doesn't these days?) but I still want the super-slick context-sensitive menu subscribe functionality available to those luddite Internet Explorer users. So I built it.
At some point I'll get approval for a new project on mozdev and will post the package to the Firefox extensions site, but in the meantime you can save it from here.
Feedback will be appreciated. Probably.