ChromEdit

ChromEdit is an extension that provides a straightforward user profile file editor. This software grants access to userContent.css, which adds user styles that are applied to webpages, and userChrome.css, which overrides UI styles. Moreover, it allows read-only access to prefs.js and access to user.js to make more permanent preference changes. However, to use user.js, users must understand the structure and possible values first.

One thing to note is that since ChromEdit is a basic ASCII editor, users should not expect fantastic features. For instance, there's no styling for menus to disappear when selected by their labels in non-English locales where accents are prevalent. A superior selection approach would be selection by ID; however, this approach requires DOM Inspector or XUL source knowledge.

Overall, ChromEdit is a decent extension that provides basic functionalities to edit user profile files. It is easy to use, but users shouldn't expect advanced features beyond the basics.