I understand color management very well, thank you. I have profiled and edited profiles for dozens of devices, from pre-press to proofing and through to production: litho, toner, wide-format UV, solvent, aqueous, and latex. Also displays, scanners, and DSLR studio environments.

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.