Firefox window does not appear

I use Firefox as my default browser. When I click on a link in my apple mail it doesn't appear but when I right click to check the Firefox icon, it shows that a window should be open (call it mystery window). In the photo it's the "Settings". I cannot seem to access it. (It used to be that if I clicked it, it would open.) If I right click the icon I can open a new Firefox window but the one I originally tried to open still does not appear. That's how I opened this page. If I've opened a new window and I right click and select "Show all Windows" I can see the original window but I still cannot access it. I've tried quitting Firefox and shutting down my computer but when I restart my computer the Firefox icon still shows that the mystery window should be open. Still cannot access it.

This is a fairly new problem that started sometime in the last few months. i have an Apple computer.