- AdBlock. Lets you switch off the annoying flashing adverts.
- Web Developer. If you’re developing web sites, you need this to understand how your web pages really work.
- View Cookies. A simple but useful tool if you’re developing web sites.
- Live HTTP Headers. Shows you what really happened under the hood. Again, more useful for web site developers.
- Show Anchors. Really handy for linking to some particular piece of a web page instead of the page as a whole.
The other extremely handy extension is the DOM Inspector, but that’s more of a builtin thing than an extension.