This is what I’ve read online..
The issue is that older versions of MacOS don’t work with the latest versions of Firefox. Firefox has two main ways of updating the browser. For compatible computers (eg running latest OS) you get regular updates. The ‘esr update channel’ is usually for enterprise that doesn’t want regular updates so gives periodic updates that are stable. It seems that you can get put on this way of doing things when you are running an older OS, meaning you won’t get the latest versions of Firefox as they don’t work with your OS. This then means that you get this update message and can’t use TvGo via Firefox (unless you update your MacOS). The good news is that Safari does work with TvGo, even on some older versions of MacOS.
If your OS is compatible with the latest versions of Firefox and you’re still getting the ‘update’ message, it means you’ve accidentally downloaded the ‘esr’ way of updating Firefox. You can change this to the ‘regular’ Firefox (which gives the updates needed for TvGo to work) by googling online instructions (backing up your Firefox settings then deleting Firefox, then installing the regular version of Firefox, then updating that with your saved backup settings).