Check out the screen shot:
(Apparently Firefox isn't liking House Whiteboard...)
I've seen this on my netbook as well which is running Firefox 3.6.8 with a screen resolution of 1024x600. However, preforming a hard refresh seems to do the trick when it happens so it might be an issue with the style sheets not getting downloaded correctly (i.e. my problem, not yours).
I have updated the css, so in case you can't load the custom font, the fall back font won't be wrapped to 2 lines. The fix will be in the next deployment.
what Browser / OS? Can't repro in Firefox current version (3.6.13) / Windows 7 64-bit: