Tip: Unexpected installation error -203 (Add-ons)

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:

  1. Close Firefox
  2. Locate your Profile Folder
  3. Delete the following files from your profile folder:
    • extensions.ini
    • extensions.cache
    • extensions.rdf
  4. 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.


Tip: Unexpected installation error -203 (Add-ons) — 18 Comments

  1. I found it was in what order you installed the Add-ons. Noscript installed first caused Netcraft Toolbar and others to fail. Uninstalling Noscript allowed installation. Once all extras had been installed then add Noscript and all should be well, that’s my experience anyway.

  2. Another thought: malware prevention apps may interfere. Above tip did not help me, so I completely wiped and reinstalled FF3. Some add-ons installed, some gave me -203 error. My malware apps run so silently (Nod32 and ThreatFire) that I forget that they are there. I turned off Threafire, and all add-ons installed without a problem. After install, turned ThreatFire back on and FF runs perfectly.

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  4. The 203 error is a common problem for all Firefox users when we try to install extensions on the browser. My problem was solved with the steps suggested by Empowered SEO blog read more on 203 error.
    Another option to remove ‘Unexpected installation error -203’.

  5. Brilliant, I managed to re-use my addons in Windows 7 deleting these 3 files (extensions.ini, extensions.cache, extensions.rdf) located in %USER%/appdata/Roaming/Mozilla/Firefox/Profiles.xxxxx.default.Thanks a lot!

  6. To everyone who is having difficulty installing add ons in Firefox.

    After updating Java to solve an unrelated problem I found that the issue with installing add ons was also resolved. Try it and see if it works for you.

  7. Thank you, this worked like a charm. I had lost all of my extensions after the last FF update to 3.6.3. I never realized how much I depended on those. Thanks so much for posting this easy fix!

  8. I tried to download No script in 3.6.3 n in 3.5 Firefox but it was not working for me then I read this blog deleted file with the extension rfd and noscript pop up by its own when I restarted fir fox

  9. looks like no one but me isn’t finding the 3 files within the Profile Folder. they just AREN’T there. what do I do? is that bug or something?

  10. This worked like a charm! I finally have NoScript installed on my PC. Thanks so much for posting this simple solution to my problem!

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