7 Add-ons in this Collection
Firebug by Joe Hewitt, Jan Odvarko, others
FoxyProxy Standard by Eric H. Jung, groeg, others
FoxyProxy is an advanced proxy management tool that completely replaces Firefox's limited proxying capabilities. For a simpler tool and less advanced configuration options, please use FoxyProxy Basic.
Add, modify and filter the HTTP request headers sent to web servers. This addon is particularly useful for Mobile web development, HTTP testing and privacy.
HTML Validator is a Mozilla extension that adds HTML validation inside Firefox and Mozilla. The number of errors of a HTML page is seen on the form of an icon
For Online HTML 5 validation, you need 0.962