This error on quitting FF even when ALL add-ons disabled:

A few minutes ago I posted a question asking what addon causes this error, but that question does not appear in my Profile Questions list so I cannot update that... THIS CONSOLE ERROR ON QUITTING FF EVEN WHEN ALL ADDONS DISABLED 8/8/14 3:54:30 PM [0x0-0x251251].org.mozilla.firefox[4505] 1407527670934 addons.manager ERROR Exception calling provider shutdown: [Exception... "Component returned failure code: 0x80004005 (NS_ERROR_FAILURE) [nsIObserverService.removeObserver]" nsresult: "0x80004005 (NS_ERROR_FAILURE)" location: "JS frame :: resource://app/modules/experiments/Experiments.jsm :: this.Experiments.PreviousExperimentProvider.prototype<.shutdown :: line 2186" data: no] Stack trace: this.Experiments.PreviousExperimentProvider.prototype<.shutdown()@resource://app/modules/experiments/Experiments.jsm:2186 < callProvider()@resource://gre/modules/AddonManager.jsm:192 < AMI_unregisterProvider()@resource://gre/modules/AddonManager.jsm:851 < AMP_unregisterProvider()@resource://gre/modules/AddonManager.jsm:2329 < Experiments.Experiments.prototype._unregisterWithAddonManager()@resource://app/modules/experiments/Experiments.jsm:500 < Experiments.Experiments.prototype.uninit<()@resource://app/modules/experiments/Experiments.jsm:446 < TaskImpl_run()@resource://gre/modules/Task.jsm:282 < TaskImpl_handleResultValue()@resource://gre/modules/Task.jsm:338 < TaskImpl_run()@resource://gre/modules/Task.jsm:290 < TaskImpl()@resource://gre/modules/Task.jsm:247 < createAsyncFunction/asyncFunction()@resource://gre/modules/Task.jsm:224 < Spinner.prototype.observe()@resource://gre/modules/AsyncShutdown.jsm:320 < <file:unknown>