An inability to install an extension can be the result of problems with the extension, or the version of Thunderbird you are using. This article describes various causes of install problems and what you can do to address them.

Add-on is not compatible

An internal file in each add-on indicates the range of Thunderbird versions with which the extension is compatible. In the Thunderbird Add-ons area of Mozilla, you can review version compatibility information on the page for each available extension.

If your installed version of Thunderbird does not fit within that range, installing the add-on results in an error, indicating that the add-on is not compatible. If your version of Thunderbird is incompatible with the add-on, you can:

• Update to the latest version of Thunderbird. For more information, see Update Thunderbird to the latest version.
• Find a version of the add-on that is compatible with your version of Thunderbird. The Thunderbird Add-ons website usually has the most up to date version of each add-on.
• Use a different extension. For many extensions, there are similar extensions that provide the same functionality. For more information, see Thunderbird Add-ons.

Add-on has a high risk of causing stability or security problems and can't be installed

Certain add-ons have been blocklisted for being unsafe. For more information, see Why does Mozilla disable some add-ons from running in Firefox?.

You are asked to download the add-on, rather than installing it

Some websites serve add-ons as downloads, requiring you to download the file to your computer, before installing it.

• These files are usually .xpi or .jar files.

1. Download the file to your local computer.
2. Click the menu button , click Add-ons and themesExtensions and themes and select Extensions.
3. To add the downloaded add-on to the list of available add-ons, drag and drop the file into the Add-ons window. The add-on is added to the list.
4. The installation process should begin.

Corrupt extension files

Corrupt extension configuration files can cause problems when trying to install an extension. Deleting these files will make Thunderbird recreate them (removing any corruption) the next time it starts. You won't lose your extensions or their settings by deleting these files.

1. To open your profile folder:
2. • Click ≡ > Help and select Troubleshooting Information. The Troubleshooting Information tab will open.
   • Under the Application Basics section, find the Profile FolderProfile Directory row, then click on Open FolderShow in FinderOpen Directory. A window will open that contains your profile folder.Your profile folder will open.
   Note: If you are unable to open or use Thunderbird, follow the instructions in Finding your profile without opening Thunderbird.
3. Delete the following files:
   • extensions.sqlite
   • extensions.sqlite-journal (if found)
   • extensions.ini
   • extensions.json
4. Restart Thunderbird.

Conflict with other extensions

Another installed extension may interfere with the installation of new extensions. Install the new extension in Thunderbird Safe Mode as a workaround.

Based on information from

• Unable to install add-ons (extensions or themes)
• Unable to install themes or extensions - Firefox (mozillaZine KB)