• cliget, Download login-protected files from the command line using curl, wget or aria2.
• Link Gopher, Extracts all links from web page, sorts them, removes duplicates, and displays them in a new tab for inspection or copy and paste into other systems.
• Link Redirect Trace, Perform advanced, comprehensive and most important correct analysis of links, redirects, and REL-canonicals. Use this extension for your SEO analysis, On page SEO, Off page SEO, competitor analysis and more.
• IPvFoo, Display the server IP address, with a realtime summary of IPv4, IPv6, and HTTPS information across all page elements.
• URLs List, List the URLs of all tabs from the current window as copyable plaintext. Also this extension can load a plaintext list of urls to individual tabs.
• Uppity, Navigate up one level (directory). It will remove an in-page anchor, the querystring, the file, and the last directory in that order, whichever is first found…
• SixOrNot, SixOrNot shows the IP (IPv4/IPv6) addresses for servers Firefox talks to to load web pages, alongside the DNS record information for those hosts. It also shows proxy configuration and a count of page elements loaded for each host.
• The Mass Downloader for your browser|DownThemAll!
• Exif Viewer, Displays the Exif and IPTC data in local and remote JPEG images.
• Wappalyzer, Identify technologies on websites
• Tamper Data for FF Quantum
  • Monitor live requests
  • Edit headers on live requests
  • Cancel live requests
  • Redirect live requests

Click the blue cloud in the toolbar to start tampering. When you're done, click it again to stop.

• BuiltWith, BuiltWith is a web site profiler tool. Upon looking up a page, BuiltWith returns a list all the technologies in use on that page that it can find.
• KNOXSS Community Edition, Tool for XSS (Cross-Site Scripting) discovery.
• Treeverse, A browser extension for navigating burgeoning Twitter conversations.
• User-Agent Switcher
• FoxyProxy Standard
• Wappalyzer
• HttpRequester
• RESTClient
• XSS Me
• SQL Inject Me
• FirePHP