This extension lets you install Piper voices to your computer, then adds these voices to the browser's list of available TTS voices, which can then be used by websites, apps, and by other browser extensions to synthesize text to audio.
For example, after installing your favorite voices. You can use this tool to test them out:
https://ttstool.com/soundboard.html
Piper Project home page
https://github.com/rhasspy/piper
Piper extension project page
https://github.com/ken107/piper-browser-extension