I mean to avoid as much tech talk here as possible… but if you look at images in a serious way online you should be using a colour managed browser. To my knowledge Safari and Firefox are currently the only browsers that read colour profiles. In Firefox 3.0 the setting is off by default but it can be switched on by going to about:config and changing the value “gfx.color_management.enabled” to “true”.

Of course, if you’re serious serious then you should have a calibrated monitor.