Helper for GitHub notifications in Gmail per Mu-An

Open your GitHub notifications using shift + g, or a "Visit Thread on GitHub" button in mail view. Or if you have keyboard shortcut enabled in Gmail, you can a select a GitHub notification email thread, and use ctrl + return in the list view and/or anywhere to visit the GitHub thread. More keyboard shortcuts for the mail view can be found and assigned in Firefox Extentions' "Manage shortcuts" page.