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.
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
IP Whois Lookup & Website Reviews & Rating. Display country flag indicating website location. Alexa and Norton Antivirus Site Adviser. Supported: GoDaddy, NetworkSolutions, Dotster, 1and1, NameCheap, Register, Yahoo, 123-Reg, FatCow, Enom, FastHosts.
CoLT (short for 'Copy Link Text') makes it easy to copy either a link's text, or both the link text and its URL in a format you specify. This non-invasive extension simply appears as context menu items when you right-click a link. Fully customizable!