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