FirePath is a Firebug extension that adds a development tool to edit, inspect and generate XPath 1.0 expressions, CSS 3 selectors and JQuery selectors (Sizzle selector engine).
AutoPager automatically loads next pages when you reach the end of a page. It works on a ton of sites,Google,Yahoo..
It works well with most other add-ons adblock plus, WOT and most of the greasemonkey scripts.
You can also try AutoPagerLite.
Feature rich XPath generator, editor, inspector and simple extraction tool...