Firefox Desktop Browser 71 was released yesterday.
Firefox release schedules
Firefox release calendar
Mozilla provides two release notes. One is for users and the other is for developers.
Firefox 71 release note
Firefox 71 release note for developers
The release note for developers lists news and changes on APIs or developer tools that may be used by web contents developers or firefox plugin developes.
You can get overview of the new release changes and prepare to manage influence on WebClass functions or your learning materials.
Pickup for webclass
I think there is nothing special to do for using WebClass with new firefox.
Acording to the release note, firefox has original mp3 audio decoder and play mp3 with it from this version.
Mozilla provides a faq page to fix audio and video playing issues.
And there is a summary page of firefox html5 audio and video format.