I've run into the same bug recently on Kanotix (Debian-stable + KDE
4) with Firefox 4 after installing gtk-qt-engine which is not in Kanotix
2010.05 by default.
After exiting Iceweasel one of the three CPU would consistently hang
every time at 100% until PID killed in htop.
Replacing Iceweasel with Firefox binary package from Mozilla did not
change this, in other words it does not appear to be specific to Debian
Problem disappeared after I read bug 572162 and removed gtk-qt-engine.
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