Your display colour profile is simply very different.
I get the thumbnail being brown, but the picture actually silver (in either Safari or Preview).
If I open the picture in Preview, and apply a standard sRGB to it (assign, not match), it goes brown, suggesting that your colour profile you have for your display is simply very different.
Not that Firefox, by default, is not colour aware, so will apply an sRGB colour profile to all files, regardless of what profiles are attached, thus why Firefox displays as brown. Safari is fully colour aware.
Whenever you take screen shots, the attached colour profile to the resulting image will be your display profile.
Note, the display profile, even after you change it, is typically stored in cache, so to make sure everything is applied, log out and re log in.
Try changing to the original "Color LCD" colour profile and log out and in and see if this fixes some of your issues.