State and Error Codes
The following document has a link to the code that defines the state and error codes that you might encounter in the browser console while testing a telemetry experiment.
A quick example of a log that has both a state and an error code that isn't defined:
ExperimentEntry #0::_installAddon() - AddonInstall onDownloadFailed for email@example.com, state=4, error=-2
In the above case, you would look up error=-2 and state=4 using the link below to see what each of the codes mean.