firefox slowness with xorg 6.9.0

[Roland Scheidegger]

Tommi Sakari Uimonen wrote:
> I'm using debian unstable (also tried kanotix), both have xorg 6.9.0 and 
> kde 3.5. Video card is ATI 7500. Firefox is 1.5
> 
> For reference, I have also oldish gentoo install with xorg 6.8.x and 
> it's fast. top shows that X takes only about 30% and firefox 50% cpu 
> while scrolling about:config page with mouse wheel while some other 
> window is on top of firefox. Gentoo has firefox 1.0.4 and kde 3.4
> 
> I'm just compiling firefox 1.5 to gentoo to bring the two systems 
> configurations closer to each other. Hopefully I accomplish a situation 
> where only xorg version differs, and then I really can blame xorg for 
> the slowness. It could be GTK slowness, because konqueror works fast 
> with the same setup (same website and another window on top of konqueror)
FWIW, I noticed some massive slowdowns when using firefox too recently, 
but after some digging it seems firefox 1.5 is fully to blame. The 
slowdowns only happen with firefox 1.5 or seamonkey 1.0, but firefox 1.0 
is fast. Maybe it simply has to do how it's compiled (using gtk2 and 
such), I don't know.
Some quick profiling showed this however (scrolling on a VERY slow page 
since it updated its layout, http://www.hardocp.com/):
8608     43.2107  libfb.so                 fbBlt
5168     25.9425  vmlinux                  default_idle
830       4.1665  libgklayout.so           (no symbols)
436       2.1886  Xorg                     (no symbols)
344       1.7268  libxpcom_core.so         (no symbols)
255       1.2801  libfb.so                 fbBltOne
188       0.9437  libmozjs.so              (no symbols)
157       0.7881  libgfx_gtk.so            (no symbols)
153       0.7680  libfb.so                 fbSolid
So, firefox 1.5 causes some massive use of libfb.so which firefox 1.0 
probably didn't (I did not profile firefox 1.0). As to why and how to 
fix it, no idea... My setup used radeons too if it matters (7200, 9000 
with xorg 6.9, and a x550 with xorg 6.8.2)

Roland