Extension doesn't display in Firefox / WebExtension migration

[glamrock]

Previously, the Cupcake extension would be displayed near the address bar by default. At some point, Firefox updated and the extension no longer has this default behavior. Mozilla's automated testing of extensions didn't catch the incompatibility.

Normally I'd be correcting this instead of filing a ticket, but I will instead take the approach of recreating the Firefox extension to be compatible with the new extension system. It's important to note this as the division point between Cupcake being a classic Firefox extension and becoming a new-style Firefox WebExtension. Hence, ticket. =)