firefox: input field color

Just create/edit ~/.mozilla/firefox/YOUR-PROFILE/chrome/userContent.css so it includes:

input, textarea {
   color:#000 !important;
}

personally I also like to ensure that the background is white, and make the text a dark grey so it's softer, so I have mine set to:

input, textarea {
   color:#555 !important;
   background-color:#fff !important;
}

Note: You'll need to quit and restart Firefox before the changes show up.

One alternative is to use a Greasemonkey script:

// ==UserScript== 
// @name           Style Corrector
// @author         Nufros (loosely based on Color Corrector by Erik Nomitch)
// @description    Style Corrector (by Nufros) allow you to edit colors, (...)
// @namespace      userscripts.org/scripts/show/36850
// @include        *
// @exclude        http://*.deviantart.com/*
// @exclude        http://*.myspace.tld/*
// @exclude        http://*.youtube.tld/*
// ==/UserScript==

// Visit the script's page for the full script

GM_addStyle("input { color: #bfbfbf; background-color: #222222 !important; }");
GM_addStyle("textarea { color:#bfbfbf; background-color: #222222 !important;}");