Is there an official line that Firefox is taking on this? As a novice to their development decisions, I've always wondered this myself.

I sometimes feel like I can sense when a UI is not native; it's completely useable, and I have no functional complaint, but it might just seem...off.

I felt a small bit of delight when I switched back to Firefox on my Windows machine and saw the snappy animations for new tabs and its menus. It made a kind of subconscious difference.