Google Analytics is a web analytics service offered by Google. Google analytics requiers that users add a js tracking code to their website in order to send page hits to Google Analytics. Google analytics also supported mobile analytics though android and IOS sdk's which sent Screen hits to google analytics. There was a difference between Mobile and web google analytics accounts.
Firebase is a platform developed by Google for creating mobile and web applications. Firebase introduced Firebase Analytics which would allow for analytics across Firebase applications. Analytics was preformed on the usage of the firebase account and applicatons running on it.
Google analytics GA4 as of writing was very recently released. GA4 allows for analytics across both web and mobile applications. Using again a snippit. Its worth noting that GA4 tracking methods is vastly different from Google analytics even the property types are different, the management api, and the metadata api.
The main difference between Google analytics and Firebase analytics is that they are two different applications. Each application measures difffent things.
Although it is early days it is now possible to link GA4 and Firebase, this blurs the lines between the two systems. This is still alpha and as of writing it has yet to be seen how well this will work.