Lifehacker is out with its 2009 Edition of its annual Top 10 Must-Have Firefox Extensions post. This year's list is pretty good, and has contributions from a number of the folks who post on Lifehacker. There are some older extensions on the list, and some new ones. Here are some thoughts on their favorites, and a few extensions we think should be there.

If you’re a dedicated Firefox user, you probably collect the best extensions for the browser on a regular basis. Pencil is an extension for drawing and graphical user interface prototyping that we noted won an award from Mozilla itself. It really is a fantastic tool for visually expressing ideas on the fly. Check out this WebWorkerDaily piece for a visual tour of what the latest version can do. And for many collections of outstanding Firefox extensions, check out OStatic's Firefox Superguide. 

The other day, we covered Firefox extensions for those tinkering with the new version 3 of the browser. Now, Webworkerdaily has a highly interesting addition to our list: Pencil--a Firefox extension that requires the new version 3.  "By coupling the Gecko drawing engine with the ability to display, save, and load an external canvas, together with a palette of shapes, Pencil installs an entire drawing application into your Firefox browser," notes WWD. As is true of Dia, Pencil works, in some ways, similarly to Microsoft's Visio visualization application. Check out WWD's experience with it.