For some days I use much more tabs in IceWeasel than before, so it uses about a gigabyte of RAM and so slow that I’m not sure if its tab list has data here or on distant servers. When scrolling a page, keeping an arrow key pressed led to very slow scrolling of much larger areas than expected. Fortunately, it was not due to large amount of information needed, but due to misconfigured graphics driver for the X server.
There are two useful, popular and free drivers for AMD RS690 chipset which my laptop has. Debian by default uses xf86-video-ati which stopped working a month ago (maybe now it works, but I have no reasons to change the driver again), so I replaced it by xf86-video-radeonhd which does exactly the same but with different code and configuration (if something doesn’t work, it is independent of these drivers). Then the file /etc/X11/xorg.conf consisted of this:
Section "Device"
Identifier "Configured Video Device"
Driver "radeonhd"
EndSection
(Useless comments skipped. Everything else is automatically configured by modern versions of X.Org X11 server.) This worked with nice 3D acceleration (automatically enabled in newer releases of the driver), but I haven’t noticed that 2D rendering was slow.
There are many 2D acceleration architectures for the X server – XAA and EXA are the important ones. XAA is slow for modern hardware and software, while EXA is newer and less tested (ten months ago I couldn’t use both it and 3D acceleration without having to reboot the machine just after starting any OpenGL-based program). Unlike Radeon (xf86-video-ati) the RadeonHD driver supports both XAA and EXA for this hardware and uses XAA by default. Therefore, (after reading about it in the man page of this driver) I had to add this additional line to the X server configuration file (before EndSection):
Option "AccelMethod" "exa"
After restarting the X server even IceWeasel is interactive and can be used to read long Web pages.
(3D acceleration with Radeon hardware in Debian requires also the firmware-linux package from the non-free repository; although the firmware has MIT/X11 license it is not allowed in main, probably since there only fonts do not have to include source.)
