Fix for unexpected installation error –203 Firefox addon

I have recently backed up the Firefox using MozBackup and restored it onto another profile. After the upgrade process, none of the add-ons are working and also wasn’t able to install any new extensions. It was failed because of firefox error code 203.

firefox error code 203

I did some research on firefox knowledge base and found this happens after a software update because of some corrupt extension files. Deleting them can fix a number of extension issues; they will be regenerated the next time you start Firefox.

  • Exit Firefox completely
  • Open your Firefox profile folder as mentioned below on different OS.
    • Windows Vista and Windows 7 – %APPDATA%\Mozilla\Firefox\Profiles
    • Windows 2000 and Windows XP – C:\Documents and Settings\<Windows login/user name>\Application Data\Mozilla\Firefox\Profiles\<profile folder>
    • Linux and Unix – ~/.mozilla/firefox/<profile folder>
    • MAC – ~/Library/Mozilla/Firefox/Profiles/<profile folder>  or ~/Library/Application Support/Firefox/Profiles/<profile folder>
  • Delete below three files or rename them.
    • extensions.ini
    • extensions.cache
    • extensions.rdf

And reopen your Firefox and the add on issue would have been resolved.

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2 Responses to “Fix for unexpected installation error –203 Firefox addon”

  1. Great suggestion! I recently updated my anti-virus software and it knocked out my extensions. I have been on the AV software forum and Mozilla FF forum for DAYS.
    This solution worked like a charm and all my extensions are restored.
    Thanks again – this was a huge help!

  2. never work

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