I’ve always been annoyed at Firefox insisting on switching to the current active virtual desktop when clicking a link to open in Firefox. For a long time, I had created a KWin rule to force all Firefox windows to stay on one virtual desktop. But what if I wanted to have a Firefox window on another virtual desktop? For example, a guide while playing a video game on desktop 4? That was made impossible with this method so I had to remove that rule each time I needed that and re-add it afterwards.
I recently stumbled upon a Reddit post where someone had a similar but not quite my issue. Due to the similarities however, I decided to give it a try and it works! Now Firefox always remains on its current virtual desktop!
about:config and set