These two firefox extensions are rather useful.
Mouse gestures - Allows you to navigate around the browser by holding down a mouse button and moving the mouse in a certain direction. No more moving the mouse to the top of the page to use the buttons there or create a new tab.
Blogthis- A nice little extension that adds a new option to the right click menu in Firefox. Right click on a page and choose blogthis and it pops up a box containing the URL so you can post it to your blog. Do it while you've selected some text and it pops up a box containing the text and a link so you can post it directly to your blog.