I was wondering if there is such an addon in firefox where you can test out css paths to check if they are finding the correct element? I was looking for something similar to xpather for xpath locations.
Not sure if this helps. Try Firebug. Allows you to select an item, and see what it's css path is, as well as the css currently being applied.
Can do some experimentation in the html/css right in the browser.
jQuery
With jQuery you could easily add a large red border to an element using the selector.
$(document).ready(function(){
$('#your-css-selector').css('border', '5px solid red');
});
FireFinder does exactly what you are looking for. You can evaluate either CSS, or XPath expressions, it will list the matching elements, and also draw a red border around them.
The 'Find' button in Selenium IDE is very useful for this. It uses the same method to locate elements as your tests will, so can be used to locate elements using any of the supported strategies.
Firebug (https://addons.mozilla.org/en-US/firefox/addon/1843) or Web Developer Toolbar (https://addons.mozilla.org/en-US/firefox/addon/60). Both show path.
Firefinder is great for testing selectors. However, if also you want to obtain the CSS selector for an element try SelectorGadget.