Disclaimer: I'm running a vintage laptop model from 2006
You have the most nimble user interface, when everything runs natively, closer to machine language.
Instead, you are running an operating system on your computer, and on top of that operating system, you are running a web browser, and on top of that, you are running a very heavy website named Facebook. Your computer slows to a crawl. Loading multiple tabs takes longer and longer.
It's less bling, less bloat. It renders more like a web page, rather than an operating system. Takes some getting used to, but once you memorize the steps, doing things in a different way, it's a lot quicker.
On the Pale Moon Browser, both sites render as mbasic, but on Chrome, m.facebook.com is a different design.