La liste des extensions que je trouve intéressantes et que je teste
Squared tabs, appmenu, add-on bar, small button view and many more 'old' features for Firefox 29+ (Windows / MacOSX / Linux).
All builds & changelogs on versions page!
Allows the download manager to also open in a tab or sidebar, and adds some optional display changes.
This extension allows you to manually sort (order) your folders in the folder pane of Thunderbird or automatically sort them, but in a better way. This extension also allows you to re-order accounts in the folder pane.
Contact Tabs enhances Thunderbird to give you quick access to all your contacts directly from Thunderbird's main window: Use the powerful search field to find your contacts and open them in a new tab for viewing and editing.
Clears preferences left by extensions after uninstallation
The missing Thunderbird "copy folder" feature! Copy folders or entire POP/IMAP accounts recursively to any location while maintaining folder structure.
Resizer for inline and attachment images (JPEG, PNG, BMP and GIF image formats).
All platforms are supported (Windows, Linux and Macintosh).
Extension to clean and vacuum your firefox places database.
Automatically do Archive/Copy/Delete/Move actions based on user defined rules
Open in a sidebar or in a tab and write headers directly. Simplicity, JS substitution, built-in functions, encryption, and regexp support.
You can easy modify header on each HTTP call on the Mozilla Firefox.
PixelZoomer takes a screenshot of the current website and provides various tools for pixel analysis. You can zoom into websites (up to 3200%), measure distances and pick colors with an eye dropper.
PixelZoomer requires Firefox 3.6 or higher.
This addon adds month tabs into Lightning calendar month view
This Add-on allows to have HTML temporarily allowed in the currently displayed message by only one click. When switching to another message, it'll be shown automatically again in plain text or simple html mode (if this is your default mode).
Adds a summary of mail accounts and folders to replace the account central pane and the empty folder preview