My IceWeasel slowed down to a crawl after I installed Acroread and the flash plugins, both of which need the ia32-libs 32-bit compatibility libraries.

It turns out npviewer.bin is taking up all CPU, so I just removed it: apt-get remove nspluginwrapper This also took out flashplayer-mozilla and mozilla-acroread. Well I didn't like the former anyway, and I didn't have much use for the latter.