I’ve been seeing several forum members on Go Firefox! getting the error:
Unexpected installation error -203
When attempting to install extensions and/or themes. In most cases these members have recently upgraded from Firefox 2 to Firefox 3 on the same profile. This error message can be caused by either:
- security software, which may be preventing these files from being updated
- corrupted configuration files on your computer
99% of the time it is going to be caused by corrupted configuration files on your computer. To fix this problem follow these steps:
- Close Firefox
- Locate your Profile Folder
- Delete the following files from your profile folder:
- Restart Firefox.
When Firefox restarts it will automatically rebuild the 3 files in step #3 above and should allow you to be able to install add-ons again.