i've had the same problem with all 180.* drivers (gentoo 32bit), but the new 180.35 seems to resolve this. firefox-bin works fine now without the munmap_chunk crash.
although i can't be sure if the driver upgrade alone fixed it, because portage also updated 21 other packages that day (qt-core poppler texinfo dialog libXi randrproto libXfont pixman man-pages fontforge ruby qt-sql xf86-video-vesa raptor soprano poppler-bindings imagemagick xine-lib gst-plugins-faad vlc libquicktime).
if it is the driver, thanks for fixing it