TBB still doesn't round windows in some cases

I understand TBB does something to reduce the fingerprintability of the browser window size, but apparently it isn't enough as https://panopticlick.eff.org/ says they've never seen my screen size before. I'm using the latest TBB on the latest debian stable with the dwm window manager.

Could TBB please round the size to a larger interval so that I look like a more typical user? Thanks.