On the GUI side, the only difference I see is a de-coloring of the stop/reload button. It used to be red/blue, but now it just blends with the white of the menubar. I've seen just one rendering problem, unfortunately with Blogger's Dashboard interface, so I'm writing this post in Safari. I could just try clicking the "Try the updated Blogger interface" link that's been staring at me for several months now, but that wouldn't be living up to my namesake. I think I'll deploy a corollary of my tried-and-true life strategy Ignore It Until It Goes Away. In this case, I'll Wait It Out Until It Comes Back. I'm sure it'll work.
UPDATE: The Blogger problem is a Firefox problem, not just TenFourFox.