I had high hopes for this but in its current state, I rarely use it. Firefox needs a split screen mode like Vivaldi, where any tab can be split into 2/3/4 screens. Let's start with 2 for now but allow us to remain in our session and not log us out. Let the page not reload just for opening it in a split view.
Allow us to split screen an .html file (that I open from my Desktop) with a on-the-Internet tab.
I really want a real split screen add-on, one that also would let us resize to our heart's content and not be limited as we are now.