Step 1: Enter about:config into your address bar

Step 2: In the filter box, type in this string:

gfx.color_management.enabled

Step 3: Now toggle that from false to true, and then restart (or close, and then open back up) Firefox.  Your done!  Now where is the catch?  Here is the explanation from Lifehacker:

From there on in, your photo colors will be richer than they were. Why isn’t this value true by default? Well, according to Mozilla, you’ll see a 10-15% performance hit using this setting, but if you’ve got a reasonably fast machine, it’ll be worth the better-looking photos. Hit the link below for an extended explanation of Firefox’s color profile support.

So, the clift notes version would be if you have a slower machine, you may not want to enable this setting.  If you have a powerhouse though, go at it.