There are no surprises (for me, at least!) that Firefox has been downloaded more than 14 million times in just 7 days!!! I am a die-hard fan of Firefox since quite a few years, and I have experienced it getting better and better over the last few years.
Today, in this post, I will share some of the tips and tricks which I personally just can't do without. In fact, they are probably the biggest reason why I love and use Firefox in the first place.
1. First things first... faster browsing!
Type about:config in the Location Bar and hit enter. Located the following and change the values...
network.http.pipelining = "true"
network.http.proxy.pipelining = "true"
network.http.pipelining.maxrequests = 30
Right-click anywhere and select New-> Integer. Name it “nglayout.initialpaint.delay” and set its value to “0″. This value is the amount of time the browser waits before it acts on information it receives.
Read More...
2. Shortcuts - Really smart and nifty Keyboard Shortcuts
Press ' and then type the link that you would like to reach.
Press / and then type the text that you would like to reach. AWESOME, AWESOME stuff. I love this part.
Ctrl + T -> New Tab
Ctrl + N -> New Window
Select Tab (1 to 8) -> CTRL + (1 to 8)
Select last tab -> Ctrl 9
Delete Selected Autocomplete Entry -> Del
Location Bar -> F6
Alt + Left arrow -> Back
Alt + Right Arrow -> Forward
F11 -> Full Screen
3. Shortcuts - A cool set of Mouse Shortcuts
Double Click on Tab bar -> Opens a new Tab
Middle Click on tab-> Closes the Tab
Ctrl + Click on link -> Opens in new Tab
Shift + Click on link -> Opens in new Window
Ctrl + Scroll up -> Zoom In
Ctrl + Scroll down -> Zoom Out
4. Search Shortcuts
Let's say you do a lot of searching for KB articles at http://support.microsoft.com. What you need to do is...
a. Browse to http://support.microsoft.com
b. Right click on the search box that you see on the page and select... Add a keyword for this search.
c. Fill it in as follows...
d. Now whenever you want to search support.microsoft.com site, all you have to do is... F6 (to go to the Location bar), type kb followed with your search string. You don't need to navigate to the page, provide search string and hit enter. Thus you save 1 full page request!!! How cool is that?
5. Search Suggestions
You have a pretty good control on how the search suggestions should behave. In fact, you can turn it off altogether.
Know more...
6. Add-ons
There are plenty of Add-Ons for Firefox and it doesn't really cause all that weird crashes even if you have a lot of add-ons. I like this feature a lot... Firefox is really smart in finding the updates and the way it installs/updates the add-ons is really cool. Even if you need to restart Firefox, it is intelligent enough to not close the various tabs for-ever that you might have had at the time of restarting Firefox. It re-spawns itself, and restores your browsing session.
7. Working with RAM
Limit RAM usage. If you find that Firefox is taking up too much memory on your computer, you can limit the amount of RAM it is allowed to use!
Go to about:config, filter for browser.cache and select browser.cache.disk.capacity. It’s set to 50000 (KB) by default, but you can lower it, depending on how much memory you have. Try 14000 if you have 512MB RAM.
Reduce RAM usage when Firefox is minimized.
Go to about:config, right-click anywhere and select New-> Boolean. Name it config.trim_on_minimize and set it to TRUE. You have to restart Firefox for these settings to take effect.
8. Delete your last visited link by pressing delete
Press F6 to go to your Location Bar. Start typing the address that you would like to delete. Once you see that Address, select it using your arrow key and press Delete button. 
9. Built-in Master Password support -> WOW!!!!!
This is pretty intuitive, but in case you would like to read more, click here.
10. Reset Master Password (in case you forget!)
This is another killer feature I guess. In case you forget your password, just type this in your location bar... It will ask your permission to reset the master password. As you would guess, Firefox is really smart, and deletes all the saved password when it resets the master password.
chrome://pippki/content/resetpassword.xul
Download Firefox (if you still haven't) and enjoy !!! 
Cheers,
Rahul
PS: A sincere request. Please don't start a debate on which browser is better. Specially Internet Explorer vs Firefox! The reason why I am asking you to not compare is simple... if you don't like a software, just don't use it. Let the developer's know in the form of feedback, and carry on. If some body is listening, you will definitely see some betterment over time. All said and done... it's a war out there... the BIG BROWSER war and it has never been easy!!!
