Delete the files extensions.* (extensions.rdf, extensions.cache, extensions.ini, extensions.sqlite) and compatibility.ini in the Firefox profile folder to reset the extensions registry. New files will be created when required.

See "Corrupt extension files": http://kb.mozillazine.org/Unable_to_install_themes_or_extensions

If you see disabled, not compatible, extensions in "Tools > Add-ons > Extensions" then click the "Find Updates" button (in Firefox 4: right-click the extension -> "Find Updates") to do a compatibility check.

See also:

• http://kb.mozillazine.org/Corrupt_localstore.rdf
• http://kb.mozillazine.org/Preferences_not_saved

The problem was not being unable to install themes or extensions. I can install them (or reinstall them) just fine.

Deleting the various extension files (.rdf, .ini, .cache, sqlite) as directed, does not reinstall extentions. The files which are recreated are essentially new and therefore empty. This process does NOT restore extensions which an upgrade has deleted and removed from firefox.

In the Tools > Add-ons > Extensions area, I had a few dozen extensions installed prior to the 3.6.13 upgrade, and now, after the upgrade, I find there is only one extension in the list.

The problem seems to be that the extensions themselves were deleted during the automated upgrade process to Firefox 3.6.13

This is something an upgrade should not do.

None of the information posted above is a remedy for this situation, and simply does not apply - there is no problem installing extensions, the localstore.rdf is not corrupt, and preferences file is not corrupt and does not enter into this.

I have read each article, I have gone through the processes outlined in each and none have applied or resulted in any kind of restoration, as none has been applicable.

It does appear the upgrade has deleted the extensions, while they are listed in the extension.cache file, which I will most likely use as a reference to recover and reinstall them.