Are you a big fan of Google’s custom search feature, which allows you to customize your own search engine to fit your needs?  The Custom Google Search add-on for Firefox, in that case, is a perfect companion. 
In a nutshell, this extension for Firefox allows you to create, use and mange your own Google Custom Engines from within the Firefox browser interface. 

You can pick up the Custom Google Search add-on for Firefox on the Firefox Add-ons web [...]

Want to have the power of your bookmark collection right at your fingertips?  SiteLauncher will allow you to assign keyboard shortcuts to all your favorite bookmarks.

To launch, all you have to do is hit Ctrl+Space (or for the Mac users Ctrl+Alt).  If you want to use it without the graphical launcher above, use Shift+Alt (or Shift+Ctrl for the Mac users).
Some of the best features include the ability to customize the appearance, set the launcher to open in current or new [...]

Need a few more handy extras with your Firefox install? Well instead of finding a lot of tiny extensions to do your tasks, why not give the Handy Xtra Stuff extension a shot?
Adds some handy extra toolbar and other functionality to Firefox, including: Custom webpage source viewer button + configuration dialog, Toggle online/offline button, Tabbar customization UI, Copy ALT/TITLE text menu options, Popup ALT text option.
+ Download and Install the Handy Xtra Stuff Extension for Firefox!

I have screwed up a number of times and have added words the dictionary that I wanted to correct the spelling of. Is there anyway to make sure this misspelled word doesn’t show up as a word any longer? Yes, you can edit your corrections to the dictionary. Just look here:
Documents and Settings\Application Data\Mozilla\Firefox\Profiles\.default\
Now find the file called “persdict.dat”. Open that up in a text editor, delete the words you don’t want in there, and then restart [...]

While using Firefox, have you ever felt the need to add your own custom toolbar buttons to the browser? When you are using Firefox, customization is a major part of the game. With the Custom Buttons extension, you can gain even more customization power over one of the most popular browsers in the market today.
[Learn More About Custom Buttons!]