Firefox 3.5.5 Add-Ons Problem

After upgrade your Firefox to version 3.5.5, you may face the similar problem when you are trying to update or install new addons or plugins into it. I found a simple solution to solve this problem.

1. Close your Firefox.
2. Go to your Profile folder. Start > Run, then type %APPDATA% and press OK.
3. When the folder popup, choose Mozilla - Firefox - Profiles. Double click on the folder inside the Profiles folder.
4. Rename the following files:
   - extensions.cache to extensionsOLD.cache
   - extensions.ini to extensionsOLD.ini
   - extensions.rdf to extensionsOLD.rdf
   - compatibility.ini to compatibilityOLD.ini
5. The renamed files will be recreated when you open the Firefox.
6. By now you should be able to install any addons for Firefox.
   

Actually you can choose to delete the above files rather than rename them. However, better just keep the old files for some safety reason.

For further reference:
1. http://support.mozilla.com/en-US/forum/1/494891
2. http://kb.mozillazine.org/Profile_folder