- FireStorage Plus! is an extra panel to Firebug for displaying and manipulating the web storage containers such as localStorage and sessionStorage.
- Arboreal is a #Firebug extension for DOM tree visualisation
- FirePath is a Firebug extension that adds a development tool to edit, inspect and generate XPath 1.0 expressions and #CSS 3 selectors.
- FirePHP enables you to print to your Firebug Console using a simple PHP function call. All data is sent via a set of X-FirePHP-Data response headers. This means that the debugging data will not interfere with the content on your page. Thus, FirePHP is ideally suited for AJAX development.
- FireQuery adds a collection of jQuery-related enhancements to Firebug. Recommended for all jQuery developers.
In the above list you see all the extensions that I find useful. There is, however; more extensions that look very interesting. For example, the performance extensions like ySlow.