Unexpected installation error -203 when installing add-ons
This article is no longer maintained, so its content might be out of date.
If you try to install an extension or theme, and receive the error message "Unexpected installation error -203", it is usually a result of extension configuration in your Firefox profile being corrupt or security software preventing those files from being updated.
Corrupt extension files
Deleting these files will make Firefox recreate them (removing any corruption) the next time it starts. You will not lose your extensions or their settings by deleting these files:
Open your profile folder:
Click the menu button , click help and select. The Troubleshooting Information tab will open.
- Under the Application Basics section, click on filesfolder will open. . A window with your profile
- Click the menu button and then click ExitQuit .
- Delete the following files:
- Restart Firefox.
Make sure your Internet security programs (including antivirus, anti-spyware, firewalls, and privacy programs) are set to allow Firefox. For configuration instructions for several specific programs, see the Configure firewalls so that Firefox can access the Internet article.