This is a security and stability upgrade with a few important security issues now addressed.
It is recommended that you move to the new version.
If you don't see a pop-up reminder to auto-update, simply go to the top of your browser,
tap 'Help', then check for updates. The update is available in most languages as of this post
and is being rolled-out now.
Release notes (and full downloads) can be accessed from the Mozilla page here.