For the moment, I only have a rough version of my search plugin, and so I'm only posting it here. Later it will be posted to the Mycroft site, for "official" download. For now, you can download it here (you may need to do a "Save As" to get it).
Once you've downloaded the plugin, you'll have to manually install it. For Firefox, you'll need to move that into the "searchplugins" directory in your profile. Mozilla Support will tell you where to find your profile. You'll then have to restart Firefox to have access to the search plugin.
Note: you will not have to update the plug-in until the search system reaches version 2.0 (it is currently at version 0.8b). All the updates (like recognizing new journals) take place on the server. Version 2.0 will come out when I find version 1 insufficient for my needs (so probably in a couple years).