Disconnect search addon causes error at startup

Following #32767 (moved), it seems Firefox is throwing an exception. I don't think it's too important.

1581718500372   addons.xpi-utils    WARN    addMetadata: Add-on disconnect@search.mozilla.org is invalid: Error: File re[/search-extensions/disconnect/](/search-extensions/disconnect/) does not contain a valid manifest(re[/gre/modules/addons/XPIInstall.jsm:671:11)](/gre/modules/addons/XPIInstall.jsm:671:11)) JS Stack trace: loadManifest@XPIInstall.jsm:671:11
awaitPromise@XPIProvider.jsm:228:15
syncLoadManifest@XPIInstall.jsm:750:24
addMetadata@XPIDatabase.jsm:2721:32
processFileChanges@XPIDatabase.jsm:3162:26
getNewSideloads@XPIProvider.jsm:3005:28
1581718500362   addons.xpi-utils    WARN    Not uninstalling invalid item because it is a proxy file

We may not need to do anything about this, but if there is a way we can prevent this error then that'll be even better (reducing noise in logging is helpful).

acat, what do you think? I haven't looked at the code in the stacktrace at all.