Firefox is one of best browser and there are some funny tricks that you can do with your firefox browser.These will not harm your browser and they are tested in the latest version of firefox i.e firefox 4.0
Here are Some Funny Firefox Tricks
To perform these tricks open your firefox browser and copy/paste the following in your address bar
This will show you dancing firefox.Your firefox window will automatically popup anywhere at screen.
This will open another firefox within in a new tab.So you will have firefox within firefox.