How do I register for google?
My son used the google and I cannot get registered in? How can I do so?
That's not a firefox software so firefox forum can't help with this. You need to contact Google support.
You can create a new Google account easily if you want one.
If you have difficulty accessing Google sites, please let us know what errors you get.
(If you need access to someone else's Google account, you would need to contact Google to explain why and prove your relationship to the other person. I'm not sure which article is relevant for that, because it doesn't sound like you've set up FamilyLink.)
Note that Firefox 78.15.0 is the last version for your Mac OS X platform (update channel: mozilla-mac-eol-esr1) and you will no longer receive (security) updates.
Current releases require Mac OS X 10.12 or newer.
Firefox 78.15.0 on the Mozilla CDN server: