How do I remove this redundant icon in my app switcher forever?

For some unknown reason, I sometimes have two Firefox icons in my app switcher, one is always stuck on the left, slowing or confusing me when I try to switch between apps: It slows me down enormously when switching between apps and I have no idea why it does that. It looks like some obtrusive feature meant to blend personal browsing history with professional workflows (what could go wrong?) which should be optional but never enabled by default. **How do I get rid of this redundant duplicate icon in my app switcher?**