These are the list of add-ons that are installed by default in my Firefox Browser.

Firebug – absolutely the best way to debug javascript (and therefore also ajax) in your web projects. console.log beats using alert() anyday.

Web Developer – the first developer add-on I ever installed and one that I can’t live without. Manipulate everything from styling to sessions using this tool.

Tamper Data – extremely useful tool for viewing/modifying your http requests to see what is being sent/received each time a page is loaded.

PHP Developer Toolbar – tired of opening php.net each time you want to search a function. Use this handy toolbar to save time and frustration.

It is a project that attempts to make many php functions available in javascript. As most php developers will at some point have to write some javascript, it is a very handy library.

You can find it over at http://www.ohloh.net/p/php-js.