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).
The first and only download manager/accelerator built inside Firefox!
Download all the links, movies and audio clips of a page at the maximum speed with a single click, using the most popular, lightweight and reliable external download managers.
LastPass, an award-winning password manager, saves your passwords and gives you secure access from every computer and mobile device.
(former Google Dictionary and Google Translate)
In-line dictionary for any word you point to or double-click; whole page translation of any web page in another language.
Scrolls the page smoothly when scrolling the mouse wheel (or keyboard arrows if enabled).
Signatures for Gmail, Google Mail, Yahoo Mail
Google and Zimbra contact sync for Thunderbird. (TB 24 and above NOT supported)
Copy and paste a name, phone number, address or other text from your Thunderbird address book quickly, with just a single menu click.
This theme is the skin which can change your Thunderbird like LeopardMail.
Note from Mozilla: This add-on has been discontinued. Try FXChrome instead.
Chromifox Basic is a coat of chrome for Firefox.
Add Gmail IMAP options to the account wizard. You can easily set up Gmail IMAP by this extension.