I can’t be the only victim for this… I’ve experienced it on two different machines, on two versions of Kubuntu (11.08 and 12.04).
If I go into System Settings → Application Appearance → Fonts and select “Enabled” for “Use anti-aliasing” then click “Configure” and select “Use sub-pixel rendering”, then (after a restart probably) all the fonts in the browser (Chrome, Chromium or Firefox) look absolutely horrible. I’ve spent two days on and off trying to fix this.
The fix I’ve found is to delete ~/.fonts.conf and ~/.kderc (not sure at this stage which is the culprit), log out and back in, and, hey presto, fonts are OK again.
Update: example before and after screenshots can be seen here – the top shows nice smooth fonts and the bottom, to my eye, look thin, spindly and a bit jagged.