Please open a new bug against lightning for it to show up in Default Applications. I'm not sure whether Lightning supports calendar links and such yet but that needs to work for Ubuntu 12.04 at least. You should be able to run ubuntu-bug xul-ext-lightning .
I'm looking into why Gedit is showing up since that doesn't seem to be the Right Thing at all.
Please open a new bug against lightning for it to show up in Default Applications. I'm not sure whether Lightning supports calendar links and such yet but that needs to work for Ubuntu 12.04 at least. You should be able to run ubuntu-bug xul-ext-lightning .
I'm looking into why Gedit is showing up since that doesn't seem to be the Right Thing at all.