“What's new with Firefox”: Release notes or an ad popup for Firefox mobile?
mozilla.org
2 threads
I believe this is a better link: https://www.mozilla.org/en-US/firefox/80.0/releasenotes/
There's also this link with more details about the migration from the old Firefox to the new one: https://support.mozilla.org/en-US/kb/firefox-android-upgrade...
That would be a better link, but that isn't the one that is opened automatically in a new tab when you open Firefox after an update.
It seems to have broken, substantially - it keeps closing (and asking to send a report to Mozilla) pages that worked fine the other day. Hopefully this isn't a new trend.