Hi mylo,
thanks for having a look and sharing, but i had the very same version.
Hi devil,
thanks for the hint! So i tried the next, experimental:
# apt-cache policy iceweasel
iceweasel:
Installiert: 15.0.1-1
Installationskandidat: 15.0.1-1
But: same (bad) behaviour :-(
Additionally i realized, that the pixelized rendering also occurs in iceweasel's page header tabs, not only inside the web pages.