I find myself, during testing, needing to see multiple web browsers on different configurations at the same time. The "best" option I've seen so far has been
Two.app for macOS, but it only shows two views and is not quite as robust now that it's aged a bit.
Are there any apps that are similar to this but allow you to have multiple panes so that you can view iOS, Android, Chrome, Firefox, etc. all in one browser at the same time?
Two.app functions with the left pane that is for mobile and the right pane for desktop view and, the kicker, while you browse, it keeps BOTH views in sync: