From Tools > Add-ons Manager > Plugins, the link to "Check to see if your plugins are up to date" opens https://www.mozilla.org/en-US/plugincheck/ That page says "Currently the plugin check service is only available to Firefox users". Probably related to bug 1121456, restricting plugin check to Firefox. The alternative browsers mentioned there were IE and Chrome, so it's not clear whether it was intended to block SeaMonkey, or just non-Mozilla browers. In any case, either the plugin check needs to work with SeaMonkey, or SeaMonkey should stop trying to use the plugin check.
References: https://wiki.mozilla.org/Websites/Plugincheck IRC Channel: irc://irc.mozilla.org:6697/plugincheck
Fixed via Bug 1153588
Status: UNCONFIRMED → RESOLVED
Last Resolved: 3 years ago
Resolution: --- → FIXED
Whiteboard: [fixed in Bug 1153588]
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