What is Firefox?
Firefox is a free internet browser owned by Mozilla. You can download it from http://www.mozilla-europe.org/en/products/firefox/.
There are a number of very useful developer tools available for Firefox, such as Firebug, the Web developer toolbar, Stylish, and DOM Inspector. These are useful for investigating and fixing bugs in Moodle, especially when working on themes.
A search plugin allows you to search certain websites directly from the search bar of the browser.
You can find all search plugins for Moodle at http://mycroft.mozdev.org/search-engines.html?name=moodle.