Installation

Method 1

1. In Thunderbird, open the extension manager with the Tools > Add-ons menu-bar command or Add-ons from the hamburger menu in the upper right corner of the main Thunderbird window.
2. Enter "Send Later" in the search box and hit Enter.
3. Find the "Send Later" add-on in the search results and click the "Add to Thunderbird" button. Click "OK" when prompted.
4. Recommended: restart Thunderbird when it's done installing.

Method 2 (use only if Method 1 doesn't work)

1. Download the add-on as an ".xpi" file from addons.thunderbird.net, saving it to your Desktop or another obvious location.
   * Note: download the file using Right click > Save link as, otherwise your web browser might think you are trying to install a browser extension.
2. In Thunderbird, select the Tools > Add-ons menu-bar command or Add-ons from the hamburger menu.
3. From here you can either drag-drop the .xpi file into Thunderbird, or click the gear icon at the top of the page, select Install Add-on From File..., and browse to the path of your downloaded .xpi package.
4. Recommended: restart Thunderbird after the add-on is installed.