Implement as a WebExtensions #3
Description
WebExtensions are an API for addon dev supported by Firefox and Chrome, at least.
A branch webextensions has been created to create a WebExtension version of EO Toolbar.
However, there is no way, for now, to make a toolbar using the WebExtension API.
This issue is open to document what is possible to do, and to get comments if the API evolves.
As a fallback, it is advised by Mozillians to use the addon SDK which provide facilities to make a toolbar.