Ask HN: Ideal rich web app architecture / When to use Firebase?

I am seeing a lot of hype for backend-less webapps, and I have skimmed the firebase docs and it looks super interesting. However I am having trouble understanding exactly when and how it should be used. Here are two projects I am working on:

1) I am building a web app which allows users to design embeddable forms which they can then include in their own site via a javascript include. This javascript code is included in their site's source once, and then their forms can be modified freely after that date using our web app.

However, we will be serving these forms to hundreds of thousands of visitors to our users' sites daily. Is it okay to use firebase for this? Can we read from the database without the websocket overhead? Would it be better to mirror the firebase database to a hosted backend database and then serve the forms from there?

2) I am building a social media management tool similar to buffer.com. A backend is obviously needed in order to post the queued posts to social media at the requested times. However, if we could use firebase, then we could keep our backend entirely separate from our front-end, which sounds like it might make life easier in certain ways.

I'm having trouble understanding when firebase should be used, but I'm in love with the idea of directly binding variables and form fields to database values in order to make writing the front-end more enjoyable. It's confusing though; it seems like you can totally get rid of the M in MVC by doing this.

In case it's relevant, my front-ends will be built in React and any backends would be built in Python/Flask. Thank you for helping me learn.. I apologize for my ignorance!