Extensions developed with WebExtension APIs are designed for cross-browser compatibility: to a large extent the technology is compatible with the extension API supported by Google Chrome and Opera. Extensions written for these browsers will in most cases run in Firefox with just a few changes. The process of porting an extension from Chrome or Opera is like this:
- Review your use of manifest.json features and WebExtension APIs against the Chrome incompatibilities reference. If you're using features or APIs that are not yet supported in Firefox, you may not be able to port your extension yet.
- Install your extension in Firefox and test it out.
- If you have any problems, contact us on the dev-addons mailing list or #webextensions on IRC.
- Submit your add-on to AMO for signing and distribution.
If you were relying on Chrome's command line option for loading an unpacked extension, check out the web-ext tool which automates temporary installation in Firefox for development.
You can even port your Chrome extension to use WebExtension APIs just by loading the Chrome Web Store page of the extension in a Firefox instance with the Chrome Store Foxified addon.