Have you fully utilized Firefox?

Do you know you can...

• Alt + Enter at the location bar to open that URL in a new tab.
• Delete a particular location history by Shift + Del. (especially good if you frequently view those "forbidden" sites... LOL)
• Middle-click at a link to open it in a new tab.
• Double-click at the tab bar / Ctrl + T to create a new tab.
• Middle-click on a tab to close it.
• Incrementally find texts by typing "/" + text you want to find. There will be an UI for this nice feature (known as find as you type if don't know know) in Firefox 1.0 so hopefully more people will know this function.
• Incrementally find links by typing "." + text you want to find.
• Search the text you highlighted using the content menu.
• View and edit many useful information in about:mozilla, about:plugins, and about:config (Mozilla can even use about:about which list all the "about"s).
• View selection source (select some contents and right-click to see the option). The source is showing the live DOM tree so you can even see the contents generated from JavaScript.
• View source of a page prepending "view-source:" to its URL (e.g. view-source:http://www.google.com).
• Install the nice All-in-One Gestures extension that bring mouse gesture to Firefox? Mouse gesture allows you to perform some actions (e.g. close tab) by drawing a continuous line on the browser window (e.g. draw a letter "L").
• [Append your personal best features of Firefox here]