Here is an oddball solution, the lightest way to have GNU/Linux and be able to use GUI applications like Firefox is to simply start a bare bones os install X-Server and something like dmenu, That’s it. Suckless.org, there is a lightweight dwm, a desktop window manager that you can use to tile windows and move them around and more. dmenu will be used to just launch the application. dwm is what manages the windows. Anything past that is based on what you need. It can be a fun challenge to make the most lightweight Firefox browser launcher.

For now, stick with what others have suggested. bare bones installations are usually meant for helping you single out a task and usually offer poor multitasking features until you put a lot of effort into installing and configuring more packages to a satisfying ease of use level.