*note: I am chrome user base, so you will find most of these addons are both on chrome and firefox. I always update this collections, I hope you follow it.
Blocks annoying video ads on YouTube, Facebook ads, banners and much more.
Adblock Plus blocks all annoying ads, and supports websites by not blocking unobtrusive ads by default (configurable).
LastPass, an award-winning password manager, saves your passwords and gives you secure access from every computer and mobile device.
Collector's Note For chrome user: http://bit.ly/hRRtj8 To sync between firefox and chrome
Xmarks is the #1 bookmarking and open tab add-on. Keep your bookmarks, and open tabs backed up and synchronized across computers and browsers. Mobile phones with Premium access. Utilize LastPass to sync passwords!
Collector's Note For chrome user: http://bit.ly/i1lExS To sync between firefox and chrome
Notifier for gmail, yahoo, hotmail, aol and more webmails.
X-notifier(aka WebMail Notifier) checks your webmail accounts and notifies the number of unread emails...
Supports : gmail, yahoo, hotmail, POP3/IMAP, facebook, twitter and more
Allows the download manager to also open in a tab or sidebar, and adds some optional display changes.
The extension previously known as GooglePreview. Inserts preview images (thumbnails) and popularity ranks of web sites into the Google, Yahoo, Bing and DuckDuckGo search results pages.
Collector's Note For chrome user: http://bit.ly/fF7CYQ
Shareaholic is the easiest way to share & bookmark great content from anywhere on the web from one simple ALL-IN-ONE add-on. Works with Facebook, Twitter, Pinterest, Google, LinkedIn, E-mail and 200+ additional services.
Collector's Note For chrome user: http://bit.ly/gHTXIF To sync between firefox and chrome
Expands the context menu's 'Search for' item into a list of installed search engines, allowing you to choose the engine you want to use for each search.
TooManyTabs allows you to store as many tabs as you like by adding extra rows in the Firefox! It saves your browser's space and memory as idle tabs are put aside. The extra rows also help to better prioritize and visualize your tabs.
This is a basic FireFox extension which simply scrolls the page down (and optionally up again) automatically at an adjustable rate.
TabCloud - Save and restore window sessions over time and across multiple computers.
Collector's Note For chrome user: http://bit.ly/dI0oGO To sync between firefox and chrome