This is SimpleLogin team. We have recently released the v2 of our Firefox extension and would like to share it here: https://addons.mozilla.org/en-US/firefox/addon/simplelogin/
The extension's goal is to protect your email address using email alias. The extension is fully open-source, both the extension (https://github.com/simple-login/browser-extension) and the server (https://github.com/simple-login/app). The server can be self-hosted and in this case, you can change the URL in the extension to point to your server.
This second version is a milestone for us in terms of features and usability. Please let us know if you think anything is missing (our roadmap is at https://trello.com/b/4d6A69I4/open-roadmap) or if you encounter any issue!