According to the article, the content stays, just cannot add more notes or notebooks. I followed the link to Evernote FAQ, and it says:
In keeping with Evernote’s 3 Laws of Data Protection, and to ensure that all users retain full ownership of their data, any Free user who currently has more than fifty notes and one notebook will still be able to view, edit, export, share, and delete existing notes and notebooks.
ya, firefox really needed a customizable fork. I like my tabs on the sidebar and all the extensions didn't make the experience feel native.
Hopefully this project brings more people to Firefox.