I use both regular Firefox and Firefox Focus. Focus is basically what incognito window is on PC, when you close it everything is gone. By not choosing either of them as the default browser I can open links in one or the other as needed.
Focus opens faster because it’s lighter but doesn’t have reader mode and you can’t open tabs manually. It’s mostly for opening quick links that you don’t want to poiute your main browser with cookies.
For a while Firefox tried to offer the ability to choose whether open links normally or in incognito tabs but it never worked well. Not sure if it’s an Android limitation or what.