I recently committed a patch which allows spellchecker dictionaries to be packaged up as extensions in Firefox 2. To test this patch, I created (by hand) a French dictionary extension, but never really posted how to create this kind of extension in general. To rectify this, and promote creating this new kind of extension for inclusion on addons.mozilla.org, I have created a simple webtool that will create an extension from uploaded dictionary files: dictionary-packager. Source is available if you want to run it on your own server.
I chose to write this as a webtool instead of a XULRunner app because we don’t have zipwriting capabilities yet in the Mozilla platform, and I was lazy and knew how to do this easily in PHP ;-).