@coothead
Sorry I kept deleting my message. After posting, I decided I wanted to think and decide for myself this time instead of simply asking trusted experts here about it. I wanted to do my homework before asking. Can you post those links again? I thought I kept them but can't find them now.
So, I tried the Polypane browser.
https://polypane.app/ My motivation had to do with its accessibility testing features. After using it for ten days, I concluded that it was unnecessary and annoying. There are other ways to test websites for accessibility, and there is no way around simply knowing the guidelines and testing with a real browser and devices. I also disliked its fundamental assumption about responsive design. I don't do "device breakpoints." I let contents direct its layout, so to me, resizing my browser is a feature, not an annoyance like the developer of this browser seems to insist. I didn't find the multipane browser window particularly useful.
@Jason Knight, please feel free to correct me and guide me on this as it is your specialty.