(Years ago I sort of had the same experience on Flickr, but I believe that more or less went away later for a while. It returned a couple of years ago, and I quietly switched from using Firefox on Flickr to mostly using Chrome.)
This result sort of surprises and depresses me (partly because using Chrome has its pains). My understanding is that in theory Firefox and Chrome are usually relatively neck and neck as far as performance goes, with Firefox at least competitive, and that especially on common sites Firefox should not be laggy. There are a number of things that could be causing this for me and not for other people, especially general users. For a start I'm on Linux and using Fedora's build of Firefox instead of the Mozilla build, while I think most performance comparisons are made on Windows or MacOS and use the official Mozilla builds.
(I'm also using a relatively odd Linux environment with relatively modest OpenGL and compositing support, which might hurt Firefox more than Chrome.)
(And I'm using some extensions in Chrome's incognito mode that I would expect to be sort of heavyweight, like uBlock Origin and a mouse gestures extension.)
PS: I care about this partly because I dislike some things Google does with Chrome and partly because I care about Firefox being competitive and good in general. The overall web ecology benefits when we have a real choice in browsers, and part of having a real choice is good performance.
(I also think that Mozilla fundamentally cares more about Linux for Firefox than Google does for Chrome. As a non-Windows, non-Mac user, I remember the days when I was a second class citizen on the web and I would rather like to not go too far back to them.)