I installed Firefox 3.5 the other day, and was immediately dismayed to see that whenever I looked at my photos on Flickr, they were red. At first I thought it was my monitor becoming miscalibrated, but then when I viewed everything in Lightroom, it was fine. Leif suggested I try other browsers, so I tried both Camino and Safari, and everything looked fine, which is when we determined it was a Firefox problem.
Apparently in 3.5, color management was turned on by default if the photo had any sort of tag associated with it. Changing the gfx.color_management.mode setting back to 0 fixed everything.