Firefox can run more and more better with these tips, read on internet, magazines, etc, some of them ufficially confirmed by firefox developers.

Keyboard shortcuts

It just takes a little while to learn these, but once you do, your browsing will be super fast. Here are some of the most common (and my personal favs):

1. Spacebar (page down)
2. Shift-Spacebar (page up) 
3. Ctrl+F (find) 
4. Alt-N (find next) 
5. Ctrl+D (bookmark page)
6. Ctrl+T (new tab)
7. Ctrl+K (go to search box)
8. Ctrl+L (go to address bar)
9. Ctrl+= (increase text size)
10. Ctrl+- (decrease text size)
11. Ctrl-W (close tab)
12. F5 (reload)
13. Alt-Home (go to home page)

Tab navigation

Instead of using the mouse to select different tabs that you have open, use the keyboard. Here are the shortcuts:

1. Ctrl+Tab (rotate forward among tabs)
2. Ctrl+Shft+Tab (rotate to the previous tab)
3. Ctrl+1-9 (choose a number to jump to a specific tab)

Auto-complete

This is another keyboard shortcut,it’s not commonly known but it's very useful. Go to the address bar (Control-L) and type the name of the site without the “www” or the “.com”. Let’s say “gufodellenotizie”. Then press Control-Enter, and it will automatically fill in the “www” and the “.com” and take you there - like magic! For .net addresses, press Shift-Enter, and for .org addresses, press Control-Shift-Enter.

Delete items from address bar history

Firefox’s ability to automatically show previous URLs you’ve visited, as you type, in the address bar’s drop-down history menu is very cool. But sometimes you just don’t want those URLs to show up (it's better don't ask why ).
Go to the address bar (Ctrl-L), start typing an address, and the drop-down menu will appear with the URLs of pages you’ve visited with those letters in them. Use the down-arrow to go down to an address you want to delete, and press the Delete key to make it disappear.

Add a keyword for a bookmark

Go to your bookmarks much faster by giving them keywords. Right-click the bookmark and then select Properties. Put a short keyword in the keyword field, save it, and now you can type that keyword in the address bar and it will go to that bookmark.

Speed up Firefox

If you have a broadband connection (and most of us do), you can use pipelining to speed up your page loads. This allows Firefox to load multiple things on a page at once, instead of one at a time (by default, it’s optimized for dialup connections). Here’s how:

Type “about:config” into the address bar and hit return.
Type “network.http” in the filter field, and change the following settings (double-click on them to change them):
Set “network.http.pipelining” to “true” 
Set “network.http.proxy.pipelining” to “true” 
Set “network.http.pipelining.maxrequests” to a number like 30. This will allow it to make 30 requests at once.
Also, 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.

Move or remove the close tab button

Do you accidentally click on the close button of Firefox’s tabs? You can move them or remove them, again through about:config. Edit the preference for "browser.tabs.closeButtons". Here are the meanings of each value: 

1. 0: Display a close button on the active tab only 
2. 1:(Default) Display close buttons on all tabs 
3. 2:Don’t display any close buttons 
4. 3:Display a single close button at the end of the tab bar (Firefox 1.x behavior)
   

Limit RAM usage

If Firefox takes up too much memory on your computer, you can limit the amount of RAM it is allowed to us. Again, go to about:config, filter “browser.cache” and select “browser.cache.disk.capacity”. It’s set to 50000, but you can lower it, depending on how much memory you have. Try 15000 if you have between 512MB and 1GB ram.

Reduce RAM usage further for when Firefox is minimized

This setting will move Firefox to your hard drive when you minimize it, taking up much less memory. And there is no noticeable difference in speed when you restore Firefox, so it’s definitely worth a go. Again, 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.