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.
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.
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.
A suite of tools for developers.
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
A quick restartless magnifier to debug styles and web pages.