FirePath for Firefox was developed as the Masters project of Pierre Tholence. It serves as a development tool to inspect, generate, and edit XPath 1.0 expressions, CSS3 selectors, and J Query selectors. Among other things, you can you want to evaluate an expression/selector, generate an XPath expression or CSS selector, and define the evaluation parent of an expression/selector.
Generate, edit, and inspect CSS 3 selectors and more