What makes a good extension?

In my opinion there are tons and tons of extensions out there that do “cool things” like tell you the weather.. but does anybody really have to know the weather every second of every day.. maybe but most people probably can go to a weather site each day, check the weather for the day and they are cool. I’m all for intergration but not at the cost of performance and wasting precious browser space for the weather seems a little silly to me. All this being said, I think the best Firefox extensions are ones that do actions that you might need to do over and over and over again. Mine are specifically tailored to SEO and Programming because these can be redudent tasks.

HTML Validator
TML Validator is a Mozilla extension that adds HTML validation inside Firefox and Mozilla. The number of errors of a HTML page is seen on the form of an icon in the status bar when browsing. The details of the errors are seen when looking the HTML source of the page.

Total Validation
This is like a HTML Validator above but also tests spelling, and accessbility.

Measure It
Draw a ruler across any webpage to check the width, height, or alignment of page elements in pixels.

Web Designer Toolbar
The Web Developer extension adds a menu and a toolbar to the browser with various web developer tools. It is designed for Firefox, Flock, Mozilla and Seamonkey, and will run on any platform that these browsers support including Windows, Mac OS X and Linux.

PDF Download
This extension, every time you click on a link, checks if the target is a pdf file and in this case let you choose what you want to do (open pdf file inside or outside Firefox, download it to the filesystem or view it as HTML).