Favorite Firefox Addons:
Lets you go "up" a level in the current website via the provided toolbar button, or by pressing Alt+Up arrow. The "up" is determined by trimming the last section of the URL, e.g. example.org/foo/somepage.html becomes example.org/foo/
I don't use this much, but it does come in handy every so often.
Flashblock is an extension for the Mozilla, Firefox, and Netscape browsers that takes a pessimistic approach to dealing with Macromedia Flash content on a webpage and blocks ALL Flash content from loading. It then leaves placeholders on the webpage that allow you to click to download and then view the Flash content.
This is a lifesaver. Try moving your mouse cursor over a piece of flash, then hitting the page-down key. Nothing happens, unless the flash is blocked.
In the Firefox Browser (and other Mozilla programs) you can per default configure only the setting for one internet connection. With the MM3-ProxySwitch you can manage different configurations and simply switch over between these.
I use this one on my laptop for managing proxies.
This extension enhances the Full Screen mode into a really full screen mode, hiding the remaining toolbars and statusbar and making them visible again when the mouse pointer hits an edge of the screen.
It also offers a slideshow mode, enabling @projection CSS rules in a document when full screen mode is turned on. Navigation between slides in implemented in the extension and a slide manager showing thumbnails for the slides is available through shift-F11.
I'm still trying this out, but it seems like a good idea.