From MozillaZine Knowledge Base

Extensions are small adds-ons that give new functionality to complement Thunderbird's built-in features, so that you can customize Thunderbird to fit your own individual needs.

Installation

There are two different ways to install a Thunderbird extension.

Download and then install:

• Browse to the web page that has the download link for the extension.
• Right click on "Install Now for Windows" (or whatever the download link is called)
• Select "Save link as" from the context menu. Navigate to a suitable folder for storing this download. Press the Save button.
• Start Thunderbird.
• Press the Install button in Tools -> Extensions (it's Tools -> Add-ons -> Extensions in 2.0) in Thunderbird. (In newer versions of Thunderbird, click on the "Gear" icon to access this function and others.)
• Browse to the .xpi file. Press the Okay button.
• Thunderbird will display a "Software Installation" window. Press the "Install now" button when it becomes enabled.

Note: Assuming you're using Firefox to download the Thunderbird extension, you need to right-click (rather than left-click) it to avoid Firefox thinking it's a Firefox extension that you want it to install, letting you try to install, and then complaining that it's incompatible. If you're using a non-Mozilla browser that's not an issue.

Drag and drop to the extensions/add-ons window:

• Browse to the web page that has the download link for the extension.
• Start Thunderbird.
• Go to Tools -> Extensions (it's Tools -> Add-ons -> Extensions in 2.0)
• Left click on "Install Now for Windows" (or whatever the download link is called) in your browser and drag it over the Thunderbird window in the Windows Taskbar (at the bottom of the screen). Don't release the button. After a second the windows focus should shift to the Extensions/Add-ons window. Drag the mouse to that window and release the button.
• Thunderbird will display a "Software Installation" window. Press the "Install now" button when it becomes enabled.

Sources for Thunderbird extensions

• Mozilla Addons: The best place to start. However, many extensions aren't available there.

• Addons Mirror Next best source.

• Mozdev Extension Room A backwater nowadays.

• Extension-writers' own websites:
  • Jeroen Peters' Thunderbird extensions
  • Maximum Extension (chuonthis)
  • Kaosmos website
  • Milimail project's extensions

• Extensions forum at MozillaZine: a good place to get a glimpse of new extensions being developed, or to try out new extensions before they become available at the sites listed above.

See also

• Incompatible extension
• Updating add-ons
• Extension development
• Other articles about extensions

External link

• How to change the version an extension supports
• Mozilla Add-ons blog