Monday, 21 July 2014

Unexpected Installation Error -203

How to Fix “Unexpected Installation Error -203″ Problem While Installing Extensions and Themes in Mozilla Firefox?

Unexpected Installation Error -203

Even existing add-ons also don't work. Its a very annoying problem and after getting a few e-mails asking for solution of this problem, today I decided to write a small tutorial to fix it.

So here we start the tutorial:


First make sure you are not using Zone Alarm or CA firewalls as both these firewalls are known to cause this problem.

If you are using any of them, disable it by using its system tray icon and then try to install the extension or theme. Now it should install without any problem. After the installation, you can again enable the firewall.


Most of the times, this problem occurs when you update the Firefox version installed in your system. If you have recently updated Firefox version, then delete following 3 files from your Mozilla Firefox Profiles folder:


These files will be re-created automatically when you start Firefox next time and your problem will be fixed.


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