I think in Chrome despite the browser being despicable the smooth animations add a fluidity to the browser and make it feel smoother. It's a hard thing to properly give words but it does affect the overall feeling and experience of using Firefox. There's a good reason all modern operating systems and most software add them. Heck even a lot of Firefox CSS themes add them and you can do it yourself through css although not to every single element of the browser. I remember wayyyy back even in Firefox 3 there was at least a fade in animation for tab hovering.
So I've opened this idea in the hopes we can get something like this in Firefox! Please show support if you would like this idea too!
Important considerations:
The animations if implemented must be consistant (toolbar, buttons, window decorations), fast and smooth enough to feel better than not having them at all, and they should ideally either be toggleable in the settings or respect your operating system's preference for animations being on or off.