Version 57 of our extension was submitted to Mozilla on 20-Jan-2018. We don't know when they will review it, but until that happens, it will not be available from this site. If you want to use the app, we created a provisional extension from the same source code, which is available now from our website
Gmail Notes is a basic note system for Gmail. With, you can create one private note for each of your Gmail conversations. These notes are viewed and edited in the Firefox sidebar.
Gmail Notes is not an integrated feature of Gmail, but a separate web application running on the Google Application Engine Framework. So your notes are stored separately from your Gmail data, although they are still in the Google infrastructure. And because your notes are stored in the Google cloud, you can view/edit/create them from different machines.