I am not sure if this belongs here, or if someone has already made something close to it. Note: None of these were made by me, I just found them.
by Wladimir Palant
Ad Blocker Plus:
This firefox add-on allows you to simply disable all ads on a site, without having to do it your self. It blocks text ads, flash ads, picture ads, and more. It is a great firefox add-on and I have had it for months. Simple and easy.
Add-on Extra <--- Need this.
To block all flash ads etc.
Click the one that is highlighted in red. Then add it to firefox.
by Chris Pederick
Web Developer:
Easily turn on / off cookies, resize browser, outline images etc, grab css coding, and more. This allows you to do a variety of things in a web development type area. Great for fast abilities to do certain things. Etc.
Firefox Add-on
by Finjan Softwar
Finjan secure browser for firefox.
This program allows you to see if a link / site is safe before you click it!
If a site has been suspected of malicious viruses / etc. It will not let you view the site directly, but instead take you to an area that asks you if you would like to continue. Great if you do not have a virus program installed! Does not stop you from using your favorite programs to hack, scam, etc.
Green = Safe Site
Brown / Dark Yellow / Dark Gold = Unknown / Cannot receive Data
Red = Not Safe / Possibly Not safe.
Highly recommend this!
Saved me numerous amounts of times!
FF Add-on
by Lorenzo Colitti, Philip Chee
Flash Block:
Lag on certain flash areas? Such as Gaia's new flash registration, or flash games, flash ads, anything else flash? Tired of lagging?
I have a crappy computer thus why I got this, It allows you to stop flash areas and asks you with a simple icon that you click to display the flash. If you do not want to display the flash you don't click it. Simple enough.
FF Add-on
by Tony Gentilcore
Fasterfox:
Allows you to change the performance of Firefox to make it run faster, or slower.
FasterFox for FF
by JumpKnowledge Team
CLICK! Online Screen caps!:
Don't know how to take a screen cap of an area on the Internet?
This allows you to take a screen cap of an actual page on the Internet and it will show the page AS IS at the moment you take the screen cap. This is a good add-on if you need proof of a certain area, or if you need to show a friend news from yahoo or something, but they are away for a few days or weeks. This does not work with flash on the internet due to it taking a live screen shot and not a still one. This only works with firefox, it might work with IE if you go to the website area.
CLICK! FF Addon
EXAMPLE: Screen cap using it of my old gaia account.
PAGE
Just a simple click of a button and you can save a page!
by Erik van Kempen, Noel Briggs Block Site ADD-on
Want to block a site? Use this program, Just post the url to the site in it, and either whitelist or black list it.
Fun Add-ons:

by Valadrem
Tabrenamizer
FF Add-on
Paranoid? Parents don't want you there? Etc?
Tabrenamizers can change the name of your tab to what ever you want. Easily change it back to the original content. etc.
I use it to hide my tabs sometimes, such as when I use webcammax to show my pc to people etc. Works great. Allows me to customize tabs to anything I want.
Tiny URL creator
With just a right click you can make any link a tiny url fast!
Want to preview a tinyurl before you click it? tinyurl.com's new preview thingy... Somewhere on their site you know?

by Intuit Innovation Lab I use this because my "recently closed" area isn't working.
I use it to view my previous websites visited. It records the data of where you go through your whole firefox session.
(From when you start firefox that moment until you close it, repeat.)
FF-Addon

by
richwklein,
Jon StritarWeather Add-on
forecastfox 0.9.6
Quote:
|
Get international weather forecasts from AccuWeather.com, and display it in any toolbar or statusbar with this highly customizable and unobtrusive...
|
or

by
Thomas Bertels
Forecastfox l10n
<--- I use this and it is correct a lot of the time.
Quote:
|
Get international weather forecasts from Weather.com, and display it in any toolbar or statusbar
|
https://addons.mozilla.org/en-US/firefox/addon/1122
Tab Mix plus, allows you to customize your tabs, and add cool effects.
All in one sidebar, Manage many things through a side bar area, easily expand / make mini, and make it where you can view two areas at once, (side bar extra)
k[ore] suggests:
No Script
NoScript - JavaScript/Java/Flash blocker for a safer Firefox experience! - what is it? - InformAction
or the addons.mozilla link:
https://addons.mozilla.org/en-US/firefox/addon/722
by
Giorgio Maone
Screen Grab: https://addons.mozilla.org/en-US/firefox/addon/1146
by
Andy M
Screen grab allows you to take a screen cap of a page just by clicking.
It allows you to take a screen cap of a whole page, or a portion!
Saves directly to your computer.
Just choose a name and file to place it in.