Welcome to Land of Tricks

Open link to new tab by just middle click-ing on it
Open a new tab by typing Ctrl + T and close with Ctrl + W
Reopen last closed tab with Ctrl + Shift + T
Bookmark by just clicking on the star button on the address bar
Scroll page down by hitting Space and scroll up with Shift + Space
Back and Forward with Alt + Left_Arrow and Alt + Right Arrow
Refresh Page with Ctrl + R

Here are some useful addons you may like:

Tweak Network: This addons let you customize your Max Connection and Pipelining. This is basically the tool to let you browse with faster speed bypassing your firefox default “limit”

xpi installation for: [ Tweak Network 1.3 ]

AutoCopy: This addons provides you the ability to automatically copy the texts you highlighted without using Ctrl + C. It is very convenient for Firefox daily use

xpi installation for: [ AutoCopy 0.97 ]

Ctrl+Tab: Well it is obvious what this addons for. It will let you use Ctrl+Tab function just like Windows Explorer

xpi installation for: [ Ctrl-Tab 0.20 ]

Adblock Plus: Well, some of the bloggers really wish you never know this addons. This addons block all of the ads once it is activated. You can set limitations on some sites though

xpi installation for: [ Adblock Plus 1.0.2 ]

Cooliris: This addons let you have a full screen 3D filled with images you googled. It is an interesting addons you should try.

xpi installation for: [ Cooliris 1.10 ]

source:- http://premiumtricks.blogspot.com/2009/05/mozilla-firefox-tweaks.html