The PC Gamer article's title also says "upgrade or". That's a heck of a detail to editorialize out of the title.
From the Mozilla post it cites:
After this, no security updates will be provided and you are strongly encouraged to upgrade to a supported Microsoft Windows version.
Or, if your current hardware can't handle Windows 10 or higher for some reason, you can switch to a Linux-based operating system. The vast majority of Linux distributions come with Firefox as the default browser.
I agree switching to Linux is the better option. I want to try Bazzite.