Lightbox is a simple, unobtrusive script used to overlay images on the current page.
Facebook’s new API allows web masters to check if visitors to their sites are logged into Facebook, and if they are to place more emphasis on their Facebook integration.
By using the a:visited css bug in browsers Social History can check if your visitors have been to a certain website, Reddit for example, it can then show a share on Reddit link depending on the result. There is no real need to include 20 different sharing link now!
For FireFox use:
Removes the righthand side sidebar on Facebook, really de-cluttering the site.
Changes the favicon on Google calendar to display the days date
Adds the ability to download YouTube videos directly on YouTube.
Changes Gmails favicon to alert you of new mail
Firefox add ons
Quix by Yoast
Sites that include several images in the design should consider using css sprites. Making sprites manually can be time-consuming, sprite me is an extremely useful bookmarklet that will add all selected images on any given site, and generate the required sprite and css.
Can add the after the deadline spell check to any page online, with just one click!
This bookmarklet is extremely useful, and makes Evernote even quicker and easier to use.
With one click it adds a search box for any site, handy when you’re looking for a post on a site that you just cant seem to find again.
Readability is a great service that removes all the clutter for a website, leaving the article formatted in such a way that its allot easier to read.