Rated 5 out of 5 stars

Would it be possible to add encryption options to this add-on? I'm not sure where exactly is the passwords catalog stored, but it seems to sync through all my Firefox browsers which is fine, but I would like some more control over how they are transmitted over to Mozilla Sync servers. Just for peace of mind.
Regardless, excellent add-on. I've been using it for about 3 years now, if not more.

This review is for a previous version of the add-on (2.9.6). 

You misunderstand. SPE is not a password manager. It augments the functionality of the password manager that has always been a part of Firefox. You can see more details at https://support.mozilla.org/kb/password-manager-remember-delete-change-and-import , which tells about the built-in functionality and about protecting your passwords (by default, anyone with access to your Firefox profile can get the passwords; there's a way to change that). As for where they are stored, you can read https://support.mozilla.org/kb/profiles-where-firefox-stores-user-data#w_what-information-is-stored-in-my-profile