My point is that in Firefox 4, sRGB is NOT being assumed, nor is it being assumed in Safari, or Chrome. In every browser I tested, those images are over-saturated on my high-gamut, profiled displays.
EDIT: According to my research, sRGB is the default color space on Windows only. That would explain my results. I am still amazed by this, and cannot understand why this should be so across all Mac browsers. I can only imagine this is because Windows defaults everything to sRGB, so there was no reason to implement this in-browser. Anyway, this just proves the point: Always tag your images, and don't assume the browser will default to sRGB.
Firefox doesn't assume sRGB for untagged images and graphs by default, only if you configure it on the advanced menu: http://gearoracle.com/guides/firefox-color-management/
The point of the test is to encourage browser developers to give users choices on how untagged page elements are color managed, and the right choice is to consider then in sRGB space. Firefox is the only browser that allows this via the gfx.color_management.mode switch. This is important because not all page graphics are images and there's no way to tag a CSS element, for example.