DOM Inspector is a tool that can be used to inspect and edit the live DOM of any web document or XUL application. The DOM can be navigated using a two-paned window displaying a variety of different views on the document and all nodes within.
Extension Auto-Installer is a helper for Firefox/SeaMonkey/Thunderbird extension developers: it allows automatically adding or updating browser extensions, e.g. via command line tools. This makes testing your changes easier.
Pretty-prints JSON content in the browser for easy, unobtrusive viewing.
Install Browser Extensions straight from GitHub Repositories
Markdown document viewer.
Allows to visualize formatted markdown documents in browser.
A simple add-on for extension testers, especially AMO editors and developers who plan to submit their add-ons to AMO.
Easiest way to Add and Manage Custom User Styles in Firefox.
Add, Edit, enable, disable and delete in-numerous User Style Sheets to redesign the Firefox and the Web.
A suite of tools for developers.
Foundstone HTML5 Local Storage Explorer allows for viewing, modifying and deleting of data items stored in the browser's LocalStorage. LocalStorage is a client side storage technology introduced in HTML5.
CSSsir is easy and handy tool which allows you to generate cross-browser code for main CSS- rules in a few clicks.
This CSS3 generator will be useful not only for web-masters and designers but also for common users.
KeyManager Tool: Firefox Add-on for Key Generation, Certificate Enrollment, CRL Signing, and Identity and Authority Delegation