There are always prerequisites.
HTML & CSS
Unfortunately for us all, the web browser is still an under-developed platform. It needs some sugar to make it digestible, and by sugar we're referring to frameworks.
Therefore we're using frameworks instead of developing in native web components. We'll stick to the two most popular and universal frameworks, Angular 2+ and React. Angular 2+ has massive adoption, and so does React. Additionally, React has spawned an entire ecosystem of spinoff frameworks such as Preact and Inferno which use JSX for rendering. If you're comfortable with JSX, you'll have no trouble following our React code.
Firebase is vanilla
The bright side is that after agonizing over framework decisions and just how we plan to render our browser pages, the Firebase SDK is entirely vanilla.
The Firebase SDKs also aim for parity between Node.js and the browser. Don't get us wrong... the underlying code is quite different in Node.js and the browser environment; however, the Firebase SDK provides a very similar external API in both environments, so your life just got much simpler. The Firebase calls that you make in the browser will look nearly identical to the calls that you'll make in Node.js.
And speaking of Node.js...
Cloud Functions, Google's functions-as-a-service or FaaS platform, uses Node.js. It also uses the command line.
If you're still not comfortable with the command line, don't worry. We'll take it slowly. However! Node.js is executed on a server, not in a browser. So we'll be executing Node.js locally in our test environment before shipping it off to Cloud Functions to be run in Cloud Functions' functions-as-a-service environment.
Also, some interactions with Firebase services require the _Firebase Tools_ah command-line interface or CLI. Firebase Tools is not particularly complicated... but it does use the command line.
Every developer needs to get comfortable with the command line at some point. Today is a golden opportunity!