Hidden Screen Source/Web Browsers?

Happy Holidays Team!

I’m in between an amateur and pro user and always finding things that I’m not sure about. Usually I can figure them out, however this issue is stumping me.

I’ve been playing with multiple screens as well as using the Web Browser feature and I stumbled upon what looks to be a lot of open web browser windows running the background. They are not actual windows though as they can only been seen when you swipe up for Mission Control I don’t use multiple desktops usually so I’m just now noticing this, however, they see to be growing in numbers. it started with just one or two and now there’s a lot more.

I have deleted the screen and web sources as well as deleted the associated layers and they are still there like a remnant ghost of days past. Pictures below.

  1. What is this?
  2. How do I close them?
  3. Does this affect performance?

Macbook Pro Mid 2014
Quad Core 2.5 GHz i7 with 16GB RAM
Catalina 10.15.7

Update… I may not need a response other than the performance question, however after a restart only a lone web browser screen appears.

I’m assuming that while multiple shows get opened or switched between, while the program is still running, it’s some sort of history or cache of the web browser working in the background.