Okay since Firefox 3 was released today, it is a color managed browser. But it is not on by default. Here is a add-on which enables it so you do not have to goto about:config and enable the color managed feature
https://addons.mozilla.org/en-US/firefox/addon/6891
If you do not want to login then just go to the developer's website
http://seanhayes.name/2008/06/16/color-management-04/
Here is a website to test and see if your browser is color managed.
http://www.color.org/version4html.xalter
Difference between a unmanaged and managed browser
http://ejohn.org/blog/color-profiles/
And here is some info if you want to do it manually.
--To enable it you must set gfx.color_management.enabled to true (via about:config) and restart Firefox
https://addons.mozilla.org/en-US/firefox/addon/6891
If you do not want to login then just go to the developer's website
http://seanhayes.name/2008/06/16/color-management-04/
Here is a website to test and see if your browser is color managed.
http://www.color.org/version4html.xalter
Difference between a unmanaged and managed browser
http://ejohn.org/blog/color-profiles/
And here is some info if you want to do it manually.
--To enable it you must set gfx.color_management.enabled to true (via about:config) and restart Firefox