Will Firefox support live captions for videos that does not have a closed caption option? This support is now available in Chrome with Windows 10 support. Will Firefox follow suit?
At this time there is no timeline when Mozilla will support live captions for Firefox. There was previous work done but that was a long time ago (source: https://bugzilla.mozilla.org/show_bug.cgi?id=1232476) and no updates have been made since then.
While there is no way to provide feedback to the developers through the browser (Help > Submit Feedback) at this time, you can use these other communities to make known your request:
Reddit : https://www.reddit.com/r/firefox/
Twitter : https://twitter.com/firefox
Facebook : https://www.facebook.com/Firefox
I hope this answers your question!