edited the readme to include FF4 in supported browsers.

README.md

@@ -25,10 +25,10 @@ Note: the actual image file does not need the ".r" in its filename. The .htacces
 As soon as rwd-images.js loads, it inserts a BASE element into the head of your page, directing all subsequent image, script, and stylesheet requests through a fictitious directory called "/rwd-router/". As these requests reach the server, the .htaccess file determines whether the request is a responsive image or not (does it have a ".r.png", ".r.jpg" extension?). It redirects responsive image requests to rwd.gif (a transparent 1px gif image), while all non-responsive-image requests go to their proper destination through a URL rewrite that ignores the "/rwd-router/" segment. When the HTML finishes loading, the script removes the BASE element from the DOM (resetting the base URL) and sets the image sources to either their small or large size (when specified), depending on whether the screen resolution is greater than 480px.
 
 ### Supported Browsers 
-Safari (desktop, iPhone, iPad), Chrome, Internet Explorer (8+), Opera
+Safari (desktop, iPhone, iPad), Chrome, Internet Explorer (8+), Opera. Firefox 4
 
 ### Support Caveats: 
-Firefox, IE 6/7, etc
+Firefox 3.6-, IE 6/7, etc
 ##### Note: 
 Unsupported browsers still receive responsive images; the drawback is that both image sizes are requested, so there's additional overhead on the initial request on the desktop. That aside, subsequent page visits can make use of a cookie that is set in all browsers to serve the appropriate size from the start.