in the firefox add-on description it says:
This sleek todo app keeps you organized, focused, and more productive. The perfect todo productivity app is there wherever you need it: on Mozilla Firefox, Android, iPhone, desktop, browser, Gmail, Thunderbird and more!
Is says Gmail but how can I get it to Gmail? I even signed for an app in Google App Marketplace but it doesn't show up anywhere in gmail.
With our Firefox & Chrome extensions it allows you to quickly add an email as a task. Once the extension is installed, make sure it's open by clicking the TD icon, and then open up an email in Gmail (or with Chrome, email first, then click on the TD icon). On the Todoist extension window, click the + button at the top, and you will see an "add email as task" option at the bottom.