Cross Browser Compatibility for Ajax Web App

Web based todo list application written in PHP/Javascript/Css works great in Chrome and needs to be fixed for IE and FireFox. Firefox - most everything works as expected but has some formatting/css issues IE9 - mostly functional IE8 - Very problematic as expected Required to work perfectly in latest version of FireFox, chrome, and IE (IE8) only. I would like the CSS and Javascript to validate without throwing avoidable errors. App consists of 2 pages 1 - Login Screen 2 - Task list screen / app screen I am a developer with too much work to handle at the moment, looking for another set of hands. If you like working on this, there is much more work to be done in the future with this app, including this same exact css work on multiple themes/skins of the app which should be pretty easy once this is done the first time.