Depends on the system you are using, but the principle is the same.

First, you need to set up your profiles in about:profiles. Then, you launch these profiles with firefox -P "<profile name>" in your terminal. Once that works, you can use anything that can launch programs via keybindings. It’s easier on window managers. For example, in my Hyprland config, I have the following lines:

bind = SUPER, Z, exec, $browser -P "default"
bind = SUPER SHIFT, Z, exec, $browser -P "lesser" 

SUPER+Z launches my hardened browser (no JS), SUPER+SHIFT+Z launches my vanilla browser (JS enabled, some options turned off). The $browser variable is set to GNU Icecat, a Firefox fork.

You can create separate profiles with different settings. That means you will have to use a different profile (a separate browser instance) for some websites. I personally launch each profile with keybindings.