See the project website at https://spidermonkey.dev/ for up-to-date links on where to find information or how to connect with others developing or using SpiderMonkey.
Chat about the project occurs on Matrix at #spidermonkey:mozilla.org.
To use this Discourse like a traditional email-list, see instructions here.
If you are trying to embed SpiderMonkey into your own project, there are some
embedding-specific examples and documentation on the mozilla-spidermonkey GitHub. Feel free to ask questions here or on Matrix.