Today i had formatted my system and installed everything again due to some problems i had before. I  installed firefox and imported my backup of bookmarks and settings of Firefox i had made before using Mozbackup.

But when i  tried to install addons  like adblockplus and few more, i started to get error, “Unexpected installation error  Review the Error Console log for more details.  -203

The error was constant with every addon and I wasnt able to install any of firefoxthem. Finally i did a bit of googling and found the solution. IT seems that  one or more out of extensions.cache, extensions.ini and extensions.rdf files associated with the Firefox extensions become corrupted and hence are causing the problems with installing add-ons.

So for solving the problem, i needed to delete extensions.cache, extensions.ini and extensions.rdf . Deleting them causes Firefox to rebuild the list of installed extensions and can solve other extension problems.

So how to find these files. Try the following steps to locate these files.

1. Click the Windows Start button, and select Run.


2. Type in %APPDATA% \Mozilla\Firefox\Profiles\ then click OK.

win-rundialog3. Windows Explorer opens a folder containing your profiles.

4. Double-click the profile folder you wish to open (e.g. the xxxxxxxx.default folder). You will find the required files in that folder.

5. Delete extensions.cache, extensions.ini and extensions.rdf files.

That’s all. After deleting the files, open Firefox Again and try installing the Addons. You wont be getting the problem now.

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