You must set it up.. First choose your modeDoes firefox 3.5 automatically manage color profiles or is there a setting that you must set?
http://kb.mozillazine.org/Gfx.color_management.mode
Note that the default 2 will only render tagged images as colour managed. 1 should assume untagged images are sRGB.
Now, in about:config, point gfx.color_management.display_profile to the correct profile.
If it looks wrong after this check here
http://kb.mozillazine.org/Gfx.color_management.rendering_intent