Worked for me with Firefox 21 on Linux with Fglrx drivers, ~12fps at my window size. Firefox 23 got about 15fps in the same scenario.
Worked in normal chrome and Firefox windows for me, unless I'm missing something.
Smooth 60 fps for me on Firefox 26, OS X (stats say at 1250x702 resolution).
WinXP: Fine in Chrome, but in Firefox (23/25) on my machine there's a flickering massacre when scrolling [0]. Maybe it's sth with my GPU drivers though (but then it's weird that in Chrome it's ok).
What GPU? Modern drivers? That's definitely a driver mess, pretty hard to cause something like that to happen if you're just feeding WebGL buffers to the driver...
5-year-old ATI Mobility Radeon, drivers not so modern because they stopped issuing new drivers tens of months ago.
Works on Chrome 28.0.1500.95, on Linux with Intel graphics. That surprised me a little..
Smooth as silk on Windows 8 + Firefox 25 at 2560x1600 full-screen. Amazing.
Worked on Chrome 29.0.1547.57 beta for OS X for me.