Add-ons using the techniques described in this document are considered a legacy technology in Firefox. Don't use these techniques to develop new add-ons. Use WebExtensions instead. If you maintain an add-on which uses the techniques described here, consider migrating it to use WebExtensions.
From Firefox 53 onwards, no new legacy add-ons will be accepted on addons.mozilla.org (AMO).
From Firefox 57 onwards, WebExtensions will be the only supported extension type, and Firefox will not load other types.
Even before Firefox 57, changes coming up in the Firefox platform will break many legacy extensions. These changes include multiprocess Firefox (e10s), sandboxing, and multiple content processes. Legacy extensions that are affected by these changes should migrate to WebExtensions if they can. See the "Compatibility Milestones" document for more.
A wiki page containing resources, migration paths, office hours, and more, is available to help developers transition to the new technologies.
If you're having trouble getting the Add-on SDK up and running, don't panic! This page lists some starting points that might help you track down your problem.
Check Your Firefox
jpm searches well known locations on your system for Firefox. jpm may not have found an installation, or if you have multiple installations, jpm may have found the wrong one. In those cases you need to use jpm's --binary option. See the jpm guide for more information.
When you run jpm to test your add-on or run unit tests, it prints out the location of the Firefox or XULRunner binary that it found, so you can check its output to be sure.
Check Your Text Console
When errors are generated in the SDK's APIs and your code, they are logged to the text console. This should be the same console or shell from which you ran the jpm command.
Search for Known Issues
Someone else might have experienced your problem, too. Other users often post problems to the project mailing list. You can also browse the list of known issues or search for specific keywords.
Contact the Project Team and User Group
SDK users and project team members discuss problems and proposals on the project mailing list. Someone else may have had the same problem you do, so try searching the list. You're welcome to post a question, too.
You can also chat with other SDK users in #jetpack on Mozilla's IRC network.
And if you'd like to report a bug in the SDK, that's always welcome! You will need to create an account with Bugzilla, Mozilla's bug tracker.