After couple of weeks using Firefox after many years of Opera I might as well just surrender.
Two ways of Firefox presenting tabs overview (list and squares) are both inconvenient and feel extremely hard to use after what Opera does.
Opera shows each tab as a miniature and presents them in horizontal, easily swipable view. You can swipe between those miniatures very fast. The speed is very important here as well as actual readable snapshots of tabs content.
In Firefox half of my tabs miniatures are empty and every time I need to find the one I want I struggle to do it.
I love almost everything about Firefox, I love your extensions and option to disable video autoplay (main reason I turned to you). But tabs overview is such a pain I might come back to Opera after couple more weeks of struggle.