Six Essential Firefox Extensions

Can a browser make you more productive? It can if it's Firefox and you've installed these six extensions:

Auto Copy This extension performs the simplest of functions: It automatically copies selected text to the clipboard. It may not sound like a big deal, but it saves you having to press Ctrl-C every time. Hey, one less step is one less step.
FireFTP Don't bother running a whole different program when you need to FTP some files. Just click the FireFTP icon and presto: Firefox turns into a full-fledged FTP client.
Flashblock No more loud, embarassing, not-suitable-for-work Flash videos when you visit a seemingly harmless Web site. Flashblock gives you, not the site, control over when an embedded video starts playing.
Foxmarks If you work on more than one PC (and who doesn't these days?), Foxmarks automatically and efficiently keeps all your Firefox bookmarks in sync.
PermaTabs Make any tab "permanent" with just two clicks. This is great for storing the results of a Google search, keeping a site around for reference while you work on a project, or leaving an instant-messaging service like Meebo running at all times.
ScrapBook With ScrapBook you can save a Web page, a snippet of a Web page, or an entire site, making this an ideal tool for research and/or reference. It's like Clipmarks, but local.

What's your favorite Firefox extension? Tell us (and the world) about it in the Comments section.