Developing add-ons in Firefox

Debugging add-ons in Firefox

https://developer.mozilla.org/en-US/docs/Tools/about:debugging

Firefox add-on documentation

https://developer.mozilla.org/en-US/Add-ons

Home page.

WebExtensions API for developing Firefox add-on

https://wiki.mozilla.org/WebExtensions

Introduction to Mozilla's implementation of WebExtensions, a new browser extension API.

https://wiki.mozilla.org/WebExtensions/FAQ

FAQ

http://arewewebextensionsyet.com/

Implementation coverage of WebExtensions API.

https://developer.mozilla.org/en-US/Add-ons/WebExtensions

WebExtensions API documentation.

https://developer.mozilla.org/en-US/Add-ons/WebExtensions/Comparison_with_XUL_XPCOM_extensions

Migration to WebExtensions from XUL/XPCOM.

https://developer.mozilla.org/en-US/Add-ons/WebExtensions/Anatomy_of_a_WebExtension

Anatomy of a WebExtension.