Manual Tweaks with about:config
Mozilla has slyly built in a treasure chest full of expandability over four generations of the Firefox browser, most of which lies with the custom “about:” URL. But don’t take our word for it: enter “about:config” (no quotes) into the URL field and you’ll get a warning about the cornucopia of custom settings ahead -- click “I’ll be careful, I promise!” and enjoy. The less adventurous can try “about:robots” just for fun.

Fill the Screen with F11
Particularly handy for smaller screens such as netbooks and laptops, you can browse distraction-free with Firefox by simply hitting the F11 key on the keyboard. Now, Firefox takes over whatever screen real estate you have to offer, and even the toolbar vanishes -- at least until you mouse up to the top of the screen. Hit F11 again to get things back to the way they were.

Run Firefox From Inside Firefox
Ready to have your mind blown? Open Firefox and type “chrome://browser/content/browser.xul” (no quotes) in your URL field and watch as a second Firefox browser window opens up inside the existing one. And it’s not just for show -- you can actually go to websites and use it, although we’ll let you be the judge of how practical this trick really is.

Three-Finger Swipes
First introduced with Firefox 3.5, there are four useful multitouch gestures built into the browser for those of us with trackpads. They all require three-finger swipes, with up getting you to the top of a page (same as Home key) and down to the bottom (End key); a three-finger swipe left lets you browse back a page, while the same trick going right lets you browse forward a page.

Keep Favorites Close with Pin as App Tab
New to Firefox 4 is the ability to create an “App Tab” from your favorite websites -- think of it as a collapsed tab of your favorite websites so you can access them with just a click. To create one, go to the website you want to save, Control-Click on the tab and select “Pin as App Tab.” Now the tab is reduced to a small, always-available icon on the left. Control-Click again and select “Unpin Tab” to set it free again.

Use URL Bar to Switch Tabs
Also new to Firefox 4 is the ability to switch to an open tab without your hands leaving the keyboard. With a series of tabs open, start typing the name of one of them in the URL bar and you’ll see an option pop up below to “Switch to tab” -- use the Down arrow key to move there and hit Return (or Enter) to make the switch, all without ever touching the mouse or trackpad.

Relocate Tabs to Their Former Location
One of the controversial changes in Firefox 4 was taking the Chrome approach, moving tabs to the top of the URL bar. But it doesn’t have to be this way, since Mozilla also wisely included the ability to move them back to the bottom again for those of us who dislike change. Go to View > Toolbars and select “Tabs on Top” to uncheck it, and your tabs will be liberated once more. Select “Tabs on Top” again to get things up top again.