Nice feature overall!
I use adblockers, tracking blockers and other privacy tools. I noticed that that when opening a page in Side View, the blockers are not running in the Side View panel, at least not adblockes as uBlock Origin. I don’t know about the “DuckDuckGo Privacy Essentials” or “HTTPS Everywhere” add-ons. It looks as if Side View were opening a complete new blank Firefox browser, so to speak. So my concern is that it seems that in Side View opened pages privacy can be reduced if all those add-ons are not activated. Is that the case?
Having that in mind, I’m also concerned about other privacy features like “Firefox Containers”, that maintain each group of pages in a container isolated of other pages in other containers. How do yo manage that issue in Side View? Are pages opened in Side View sharing the “by default” container?