One of the reasons we released Fennec A1 with desktop versions was to allow add-on developers to start hacking on Fennec add-ons. As long as the add-on contains no binary compiled code, it should run on any platform – including mobile devices. Developers can build and debug Fennec add-ons using the desktop builds, without needing an actual device.
As I previously posted, making a Fennec add-on is no different than making an add-on for any Mozilla-based application, such as Firefox, Thunderbird or Songbird. Fennec is a different application – add-ons for Firefox will not Just Work in Fennec. I started documenting the process of building Fennec add-ons. I plan to add some use cases there too.
Fennec supports installing add-ons from websites (remember to use the right MIME type – application/x-xpinstall). Once an extension is ready for testing, the developer can post the XPI somewhere. The add-on can then be installed to Fennec on devices or Fennec on desktops.
Very soon, we will support Fennec add-ons on AMO (addons.mozilla.org)
Update: If you want to debug your code using the error console, try using the command line flag like this: