Dear Maintainer,
when rendering http://sounl.org in iceweasel, the fonts look really ugly, square pixel fonts. I found that this was due to the Helvetica font. Disabling Helvetica in the css made the page appear normal. I found that in Debian the only installed helvetica fonts are in /usr/share/fonts/X11/100dpi and /usr/share/fonts/X11/75dpi. These are bitmapped fonts.
Solution
Disabling bitmapped fonts in Debian solves the problem:
ln -s /etc/fonts/conf.avail/70-no-bitmaps.conf /etc/fonts/conf.d/70-no-bitmaps.conf
I don't know if this is the best solution, but for me it works. I think iceweasel should not use bitmap fonts because they are really ugly. It's better to fall back to another font then to use a bitmapped font in my opinion.