I hadn't yet but I downloaded it based on your recommendation and it's very cool. That being said, I'm sticking with Firefox nightly right now because I like the rounded bottom corners and theme I'm using and I just don't have that many special needs. That being said, I'll definitely occasionally use floorp and maybe after some playing with the crazy customization I'll switch.
Discussion
Cool. Floorp has a setting for rounded corners. Wonder if thats the same as what you need
OK quick update. I found that setting which is cool. It actually rounds the content inside of the window container. However I found that the firefox about:config flag that enabled round bottom corners also works in floorp so I will daily drive it for a while at least. For some reason i assumed it used too much of its' own GUI to work with that flag. Thanks for the recommendation.