This project uses the speechSynthesis web API to read Reddit comments and posts aloud.
I am pretty sure that numerous similar addons exist, and most of them probably do a better job of it than I, but my goal is not to replace them.
This project started as one-off code written in the browser console (as evidenced by the mix of jQuery and vanillaJS) to read a particularly-long TFTS post, and I am using it to experiment with both the speech API and FireFox webextensions.